The Sin Problem: 
We need to note at the very beginning of our argument that even a genuine conversion and subsequent change in our hearts will NEVER result in "sinless perfection".  While our Lord faced all of life's temptations without incident of error (Heb.4:15), the rest of us by our Adamic sinful nature will fall woefully short of the mark of absolute sinless perfection (Rom.3:23).  This is because our very inherited physical makeup is corrupt and "indwelt" by sin (Rom.7:20; Gen.6:5, 8:21).  Therefore, we must not make the mistake of "redefining" sin in order to align with our personal theology of liking.  Sin is not just what we personally find offensive, but rather everything which God has forbidden - His Laws/Commandments.  We can neither add to God's list of prohibitions, nor subtract from it with impunity.  With God, ALL sin is an offense against His Person, for all sin is in essence disobedience to His prescribed will, with no exceptions.  Adam and Eve were expelled from the garden of paradise as a consequence of their eating of the forbidden fruit, an act which does not seem particularly immoral in and of itself, but which was a clear and willful rejection of God's authority and direct commandment (Gen.2:16-17).  Actions prohibited by God, even if they may appear to be insignificant to us, are just as sinful as those which shock and offend us personally.

Hebrews 4:15 (KJV)
¹⁵ For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
 
Romans 7:20 (KJV)
²⁰ Now if I do that I would not, it is no more I that do it, but sin that dwelleth in me.

Genesis 6:5 (KJV)
⁵ And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.

Genesis 8:21 (KJV)
²¹ And the LORD smelled a sweet savour; and the LORD said in his heart, I will not again curse the ground any more for man's sake; for the imagination of man's heart is evil from his youth; neither will I again smite any more every thing living, as I have done.

Genesis 2:16-17 (KJV)
¹⁶ And the LORD God commanded the man, saying, Of every tree of the garden thou mayest freely eat:
¹⁷ But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.

The Myth of Sinless Perfection: 
Even though we have been given the charge "be ye Holy as I Am Holy" which is in and of itself a standard to which we (1Pet.1:15-16), are expected to endeavor to attain as we mature spiritually: (Heb.5:11-14), absolute sinlessness is nonetheless unattainable in this corrupt mortal body and in this corrupt world in which we are compelled to exist.  "Sinless perfection" is a false doctrine, and a dangerous one at that, because of the enormous psychological intensity it generates.  The reality and inevitability of sin most often leads its adherents to subscribe to such notions as to deny that certain categories of sin are really sin at all, or to deny that they can and do commit certain sins.  To this end, the reach of sin is so broad and insidious that it embraces the very motivations, expressions, and essence of the human heart (Jer.17:9; Gal.5:19-21; Eph.4:29-31; Phil.2:3-8).  No matter what standard of perfection we choose to try and prove our own self-righteousness, we are ultimately bound to fail (cf. Rom.9:31; 10:3).  The fundamental Ten Commandments, the most specific standard of human conduct ordained by God, concludes by pronouncing the acquisitive and lustful desires of our hearts just as utterly sinful as idolatry or murder ("thou shalt not covet": Ex.20:17; cf. Rom.7:7-12).  As such, Apostle Paul declared that God's very purpose in giving the Law was to prove to all mankind that beyond any doubt we are all sinful and therefore in need of God's solution for our inherited sin problem.  That resolution being our one and only Lord and Savior Jesus Christ (Rom.3:9-20; Gal.3:19-25).  Many of the "religious" people of Paul's day tried to use the Mosaic Law as a standard to prove their righteousness, but in doing so only managed to condemn themselves (Rom.3:20), because Salvation cannot be earned by our works.  The only true righteousness is that given us by God when we believe in His Son (Rom.4:5) and are justified by His Blood.  As followers of Jesus in a hostile world which is in the devil's grip, we cannot afford to be under any illusions about our personal foibles, errors, and sins.  We must recognize them for what they are and immediately make use of the grace God has bestowed on us to deal with these short commings/sins.

1 Peter 1:15-16 (KJV)
¹⁵ But as he which hath called you is holy, so be ye holy in all manner of conversation;
¹⁶ Because it is written, Be ye holy; for I am holy.

Hebrews 5:11-14 (KJV)
¹¹ Of whom we have many things to say, and hard to be uttered, seeing ye are dull of hearing.
¹² For when for the time ye ought to be teachers, ye have need that one teach you again which be the first principles of the oracles of God; and are become such as have need of milk, and not of strong meat.
¹³ For every one that useth milk is unskilful in the word of righteousness: for he is a babe.
¹⁴ For they that say such things declare plainly that they seek a country.

Jeremiah 17:9 (KJV)
⁹ The heart is deceitful above all things, and desperately wicked: who can know it?

Galatians 5:19-21 (KJV)
¹⁹ Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
²⁰ Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies,
²¹ Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.

Ephesians 4:29-31 (KJV)
²⁹ Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
³⁰ And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
³¹ Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:

Philippians 2:3-8 (KJV)
³ Let nothing be done through strife or vainglory; but in lowliness of mind let each esteem other better than themselves.
⁴ Look not every man on his own things, but every man also on the things of others.
⁵ Let this mind be in you, which was also in Christ Jesus:
⁶ Who, being in the form of God, thought it not robbery to be equal with God:
⁷ But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men:
⁸ And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross.

Romans 9:31 (KJV)
³¹ But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.

Romans 10:3 (KJV)
³ For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.

Exodus 20:17 (KJV)
¹⁷ Thou shalt not covet thy neighbour's house, thou shalt not covet thy neighbour's wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour's.

Romans 7:7-12 (KJV)
⁷ What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet.
⁸ But sin, taking occasion by the commandment, wrought in me all manner of concupiscence. For without the law sin was dead.
⁹ For I was alive without the law once: but when the commandment came, sin revived, and I died.
¹⁰ And the commandment, which was ordained to life, I found to be unto death.
¹¹ For sin, taking occasion by the commandment, deceived me, and by it slew me.
¹² Wherefore the law is holy, and the commandment holy, and just, and good.

Romans 3:9-20 (KJV)
⁹ What then? are we better than they? No, in no wise: for we have before proved both Jews and Gentiles, that they are all under sin;
¹⁰ As it is written, There is none righteous, no, not one:
¹¹ There is none that understandeth, there is none that seeketh after God.
¹² They are all gone out of the way, they are together become unprofitable; there is none that doeth good, no, not one.
¹³ Their throat is an open sepulchre; with their tongues they have used deceit; the poison of asps is under their lips:
¹⁴ Whose mouth is full of cursing and bitterness:
¹⁵ Their feet are swift to shed blood:
¹⁶ Destruction and misery are in their ways:
¹⁷ And the way of peace have they not known:
¹⁸ There is no fear of God before their eyes.
¹⁹ Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God.
²⁰ Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.

Galatians 3:19-25 (KJV)
¹⁹ Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.
²⁰ Now a mediator is not a mediator of one, but God is one.
²¹ Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law.
²² But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
²³ But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed.
²⁴ Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.
²⁵ But after that faith is come, we are no longer under a schoolmaster.

Cleansing from Sin: 
As believers, we have already been "washed" clean of our sins (justified), that is, forgiven and pronounced Holy by Christ's work on the Cross when we accept that work by faith (Eph.2:5-9).  Although we are clean and pure "in Christ" (1Cor.6:11), it is still possible for our feet to pick up a bit of dirt as we walk about in the devil's playground.  God has given us the status of "adopted Holy Children/Sons of God", but we are still imperfect and still capable of sinning.  We must therefore be alert to the fact that as long as we sojourn on this earth we shall always be vulnerable to personal sin, and we must be ready to confess it whenever we become entangled in the "sin which so easily besets us" (Heb.12:1).  This is the point Jesus made when He washed the disciples' feet before the last supper (Jn.13:1-17).  Peter was unwilling to allow Jesus to wash his feet along with the other disciples.  But when Jesus told him that without the washing of his feet, Peter could have "no share" in Him, Peter demanded that the Lord wash his body also.  Jesus replied, "He that is washed needeth not save to wash his feet, but is clean every whit: and ye are clean..." (Jn.13:10).  Our Lord was telling us that our release from the bondage of sin which has held all mankind under condemnation since Adam, that this release or "redemption" was provided by His death on the Cross in our place and appropriated by us through our faith in Him (Col. 2:13-14).  This is the forgiveness cleansing from sin which is required for continued progressive salvation as we mature in the Body of Christ.  Thus, as we commit acts of personal sin as believers, and we indeed do, we are in need of the forgiveness and restoration which comes to us when we confess our sins before God.  Therefore, we need to be cleansed of our sins through God's forgiveness as often as we commit them.

Ephesians 2:5-9 (KJV)
⁵ Even when we were dead in sins, hath quickened us together with Christ, (by grace ye are saved;)
⁶ And hath raised us up together, and made us sit together in heavenly places in Christ Jesus:
⁷ That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus.
⁸ For by grace are ye saved through faith; and that not of yourselves: it is the gift of God:
⁹ Not of works, lest any man should boast.

1 Corinthians 6:11 (KJV)
¹¹ And such were some of you: but ye are washed, but ye are sanctified, but ye are justified in the name of the Lord Jesus, and by the Spirit of our God.

Hebrews 12:1 (KJV)
¹ Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us,

John 13:1-17 (KJV)
¹ Now before the feast of the passover, when Jesus knew that his hour was come that he should depart out of this world unto the Father, having loved his own which were in the world, he loved them unto the end.
² And supper being ended, the devil having now put into the heart of Judas Iscariot, Simon's son, to betray him;
³ Jesus knowing that the Father had given all things into his hands, and that he was come from God, and went to God;
⁴ He riseth from supper, and laid aside his garments; and took a towel, and girded himself.
⁵ After that he poureth water into a bason, and began to wash the disciples' feet, and to wipe them with the towel wherewith he was girded.
⁶ Then cometh he to Simon Peter: and Peter saith unto him, Lord, dost thou wash my feet?
⁷ Jesus answered and said unto him, What I do thou knowest not now; but thou shalt know hereafter.
⁸ Peter saith unto him, Thou shalt never wash my feet. Jesus answered him, If I wash thee not, thou hast no part with me.
⁹ Simon Peter saith unto him, Lord, not my feet only, but also my hands and my head.
¹⁰ Jesus saith to him, He that is washed needeth not save to wash his feet, but is clean every whit: and ye are clean, but not all.
¹¹ For he knew who should betray him; therefore said he, Ye are not all clean.
¹² So after he had washed their feet, and had taken his garments, and was set down again, he said unto them, Know ye what I have done to you?
¹³ Ye call me Master and Lord: and ye say well; for so I am.
¹⁴ If I then, your Lord and Master, have washed your feet; ye also ought to wash one another's feet.
¹⁵ For I have given you an example, that ye should do as I have done to you.
¹⁶ Verily, verily, I say unto you, The servant is not greater than his lord; neither he that is sent greater than he that sent him.
¹⁷ If ye know these things, happy are ye if ye do them.

Colossians 2:13-14 (KJV)
¹³ And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses;
¹⁴ Blotting out the handwriting of ordinances that was against us, which was contrary to us, and took it out of the way, nailing it to his cross;

John's Primer on Sin:
For all the reasons mentioned above, sin is a very personal, very disturbing issue.  Writing to a congregation which, though ethnically and geographically diverse, had had the benefit of apostolic teaching for many years, the apostle John nevertheless felt the need to review at length the sin issue in his epistle we know as 1st John.  In chapter one, verses five through ten, he covers the doctrine of sin in a pithy summary:

1st John 1:5:  This then is the message which we have heard from Him, and declare unto you: that God is light and in Him is no darkness at all.

This verse states the principle emphatically that God has nothing to do with sin.  He is not the originator of it and bears no responsibility for it whatsoever.  Nor does He condone it in the least.  Sin is foreign, antithetical to God, so if we would belong to God, sin can have no place with us either.

1st John 1:6:  If we say that we have fellowship with Him, and walk in the darkness, we lie, and do not the truth.

Since God and sin are unalterably opposed to each other, we must choose whether to follow God or sin.  We cannot simultaneously follow the dark path of sin and at the same time have a relationship (fellowship) with God.  If we claim that we are enjoying a relationship with God while living under the dark power of sin, we are only deceiving ourselves and making God out to be a liar, for He tells us that He cannot accept what is sinful.  Without the power and wonder of God's grace, these two verses would be terrifying for anyone viewing themselves and their lives with an honest heart.  The words of the disciples spring to mind: "Who then can be saved?" (Matt.19:25).

1st John 1:7: But if we walk in the light, as He is in the light, we have fellowship one with another, and the blood of Jesus Christ His Son cleanseth us from all sin.

The use of the Greek word pas ("all") without a definite article suggests that John is here referring to all acts of personal sin.  For those who choose against God in this life, there is no escape from sin and therefore no fellowship with the holy people of God.  But for those who choose to walk in the light and follow Christ, God has provided a means of cleansing from every aspect of sin: the work of His Son Jesus Christ on the cross (referred to here and often in Scripture as "His blood", cf. Matt.26:28).  Because of what Jesus Christ did for us in dying in our place, the Father is justified in accepting His work on our behalf, forgiving us all our sins, and considering us clean despite the sinful nature we retain in these earthly bodies.  In the analogy, covering the sin which besmirches us God the Father sees instead "the blood of Christ" with which we "have been sprinkled" (cf. Heb.10:22).  He is satisfied that the death penalty for sin has been paid on our behalf.  He regards us as guiltless on account of our relationship with His Son rather than judging us according to our necessarily sin-tainted merits.  Note carefully in verse seven, however, that believers who are approaching the Christian life in the correct way ("walking in the light") still need cleansing from sin as part of their Christian walk.

1st John 1:8: If we say that we have no sin, we deceive ourselves, and the truth is not in us.

Verse eight is an important caveat to believers who would rather not think of themselves as sinners.  If we are unaware of committing any transgressions lately, it is most likely because we lack a clear understanding of the wide ranging and insidious nature of sin.  The Scripture here is quite clear.  As believers, we still sin.  It is true that we are commanded not to sin.  It is true that suppression of sin is a necessity for spiritual growth and even spiritual safety.  But it is also true that as long as we inhabit these imperfect bodies and reside in the devil's world, we must continue our struggle against personal sin, even resisting "to the point of blood" (Heb.12:4; cf. 1Pet.4:1).  Verse eight is written neither to discourage us to resist sin, nor to encourage us to commit it, but rather to alert us to the cold, hard reality of the situation in which we find ourselves, and to awaken us to the necessity of dealing with personal sins in the correct, Biblical way, namely, through confession of those sins.

1st John 1:9: If we confess our sins, He is faithful and just so as to forgive us our sins, and to cleanse us from all unrighteousness.

Verse nine means that God's forgiveness of our personal sins is consistent with both His faithfulness (He doesn't break His word) and righteousness (because of Christ's pre-payment on our behalf); when we confess our sins in prayer to the Father, He forgives us and restores us to full fellowship with Himself and His Son.

1st John 1:10: If we say that we have not sinned, we make Him a liar and His Word is not in us.

Confession of sin is an essential part of the Christian's daily walk.  Combined with regular self-examination, a Biblical understanding of personal sin should provide plenty of material for the average Christian to confess.  The claim of "sinlessness" is an erroneous one, and is extremely hazardous to the Christian's spiritual health (1Cor.11:28-32).

1 Corinthians 11:28-32 (KJV)
²⁸ But let a man examine himself, and so let him eat of that bread, and drink of that cup.
²⁹ For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body.
³⁰ For this cause many are weak and sickly among you, and many sleep.
³¹ For if we would judge ourselves, we should not be judged.
³² But when we are judged, we are chastened of the Lord, that we should not be condemned with the world.

Confession of Sin: 
As believers we are completely "clean" from sin only when viewed from the standpoint of our relationship with Christ.  By virtue of our "position" in Christ, God the Father considers us totally washed of our past sins, NOT FUTURE sins.  We are "clean on the inside", so to speak.  In our everyday experience, however, we frequently get "dirty on the outside".  We don't immediately cease to be Christians because we have made a mistake – we still "hold on to Christ" and so are still considered clean by God in that critical respect.  When we simply err, and ask for forgiveness, we don't need another complete "salvation bath - new birth"; only our metaphoric "feet" need washing as a result of the personal sins we commit.  However, be that as it may, it is God who ultimately decides where the line of a collapse in both one's salvation and eternal security begins.  Thus, salvation is CONDITIONAL to the continued keeping of God's Commandments... 

Confession is the solution which God has provided for this continuing problem.  Just as the work of Christ is sufficient to free us all from sin at the point of time when we believe in Him (as represented by the ritual cleansing of baptism), so that same work of Christ is also sufficient to wash us clean whenever we sin after the point of initial justification and subsequent in process salvation.

David's great psalm of confession, Psalm 32, is a model for the mechanics of confession in that it demonstrates so clearly the two most important principles to keep in mind as we face the vexing problem of personal sin.  On the one hand, we must own up to our mistakes realizing that sin is a serious business which carries with it serious consequences, and we must approach God for His forgiveness with a genuinely contrite heart.  On the other hand, we must also approach Him in the sure and certain confidence that He will forgive us immediately (although we must stop the sin), for His forgiveness is not based upon our personal merit, but upon the work of His Son, Jesus Christ.  As is often the case in the application of Christian truth, we must avoid extremes on either hand.  We cannot afford to ignore the seriousness and the wrongness of what we have done, any more than we can afford to give in to excessive guilt or uncertainty about the perfect, loving forgiveness of God.

David's experience illustrates both of these principles clearly.  When he tried to hide his sin from God, David was visited by God's stern discipline (Ps.32:3-4).  But when he "made known" or acknowledged it, "ceased to hide it and confessed" it, God forgave him (Ps.32:5).  Acknowledgment, cessation of covering up, and confession are not separate "stages" of confession, but rather different aspects of the same process of owning up to one's sin. The idea is that we need to tell God about our sins in prayer (see Ps.32:6), stopping our denial, and to admit the truth of our sin(s).  Then, when we do so, we can confidently expect God to forgive us as He did David (cf. 1Jn.1:9).  As it says in Proverbs 28:13, "The one who hides his transgressions will not prosper, but he who admits and abandons them will be shown compassion" (read also Psalm 51). 

Psalms 32:3-4 (KJV)
³ When I kept silence, my bones waxed old through my roaring all the day long.
⁴ For day and night thy hand was heavy upon me: my moisture is turned into the drought of summer. Selah.

Psalms 32:5-6 (KJV)
⁵ I acknowledged my sin unto thee, and mine iniquity have I not hid. I said, I will confess my transgressions unto the LORD; and thou forgavest the iniquity of my sin. Selah.
⁶ For this shall every one that is godly pray unto thee in a time when thou mayest be found: surely in the floods of great waters they shall not come nigh unto him.

1 John 1:9 (KJV)
⁹ If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.

Proverbs 28:13 (KJV)
¹³ He that covereth his sins shall not prosper: but whoso confesseth and forsaketh them shall have mercy.

As can clearly be seen by the presented argument and Scriptural evidence above there is no preponderance of validity whatsoever to the misguided and dangerous doctrine of "Sinless Perfection".