I believe God's Word:
1 Jn 1:5-10
5 This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all.
6 If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth:
walk in darkness this is present tense and speaks of continuous or habitual action.
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.
Walking in the light means believing what Scripture tells us.
8 If we say that we have no sin, we deceive ourselves, and the truth is not in us.
John is addressing believers throughout this chapter. The word have is present tense and signifies continuity.
The sense here in light of what follows is that our general condition is sinless because of Jesus continuous cleansing; but we do occasionally stumble into sin which if acknowledged is cleansed restoring us to sinlessness in God's eyes; but if not acknowledged is not cleansed. I believe that one confession at the time of salvation is sufficient if we accept God's word that we do in fact continue in sin which must also be cleansed.
9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
10 If we say that we have not sinned, we make him a liar, and his word is not in us.
KJV
This scripture makes a clear statement on this issue. Since Scripture does not contradict scripture, all other Scripture must be interpreted in light of this one.
I think it is important to acknowledge that this is not all John says on this issue and in fact continues via each chapter. Thus bringing clarity to his intent in this first chapter.
Even noting the first verse of chapter 2 saying:
1Jn 2:1
My little children, these things write I unto you, that ye sin not. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
The intent is that they do not sin that is why he wrote the things in chapter 1 and forward also. But those who confess their sin
have and advocate Jesus.
as for light and darkness it is explained in chapter 2 in more detail.
1Jn 2:2 And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.
1Jn 2:3 And hereby we do know that we know him, if we keep his commandments.
1Jn 2:4 He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him.
1Jn 2:5 But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.
1Jn 2:6 He that saith he abideth in him ought himself also so to walk, even as he walked.
Notice they walk as he/Jesus walked. They are like Jesus they keep the commandments, their love for God is perfected in Christ. Sin is the opposite of love thus these persons do not sin as the love of God is perfected in them.
Jn 2:8 Again, a new commandment I write unto you, which thing is true in him and in you: because the darkness is past, and the true light now shineth.
1Jn 2:9 He that saith he is in the light, and hateth his brother, is in darkness even until now.
1Jn 2:10 He that loveth his brother abideth in the light, and there is none occasion of stumbling in him.
1Jn 2:11 But he that hateth his brother is in darkness, and walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes.
light and darkness is love or lovless/sin.
But chapter 3 really makes it clear:
1Jn 3:14 We know that we have passed from death unto life, because we love the brethren. He that loveth not his brother abideth in death.
1Jn 3:15 Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him.
1Jn 3:16 Hereby perceive we the love of God, because he laid down his life for us: and we ought to lay down our lives for the brethren.
Love for each other is light and is not sin. This is in line with the commandments of God which are summed up in one word: love.
but note how John explains it:
1Jn 3:1 Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not.
1Jn 3:2 Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.
1Jn 3:3 And every man that hath this hope in him purifieth himself, even as he is pure.
1Jn 3:4 Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law.
1Jn 3:5 And ye know that he was manifested to take away our sins; and in him is no sin.
1Jn 3:6 Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
1Jn 3:7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous.
1Jn 3:8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil.
1Jn 3:9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God.
1Jn 3:10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
John is abundantly clear that Jesus gives us complete victory over sin. WE do righteousness just as He is righteous. It is Christ in us by faith through the Spirit. His seed in us causes us to not sin any more but rather the love of God perfected in us by faith in Jesus.
That is salvation friend, that is the Good news that is a miraculous work of God. We may not understand it but none the less it is reality for those who trust as a child the promises of God.
There are many witnesses to this truth throughout the bible. I don't think you can dismiss them with a few lines form one book that has much more to say than what is in chapter one. and as you know I disagree with your point as John is clearly talking to people who do not have fellowship with them yet.
Have they heard of Jesus? Yes clearly,
Do they believe? YEs clearly.
But they like Nicodemus have yet to be born again, they have yet to join the mystery of the fellowship as Paul writes:
Eph 3:9 And to make all men see what is the fellowship of the mystery, which from the beginning of the world hath been hid in God, who created all things by Jesus Christ:
What is this mystery:
Eph 3:14 For this cause I bow my knees unto the Father of our Lord Jesus Christ,
Eph 3:15 Of whom the whole family in heaven and earth is named,
Eph 3:16 That he would grant you, according to the riches of his glory, to be strengthened with might by his Spirit in the inner man;
Eph 3:17 That Christ may dwell in your hearts by faith; that ye, being rooted and grounded in love,
Eph 3:18 May be able to comprehend with all saints what is the breadth, and length, and depth, and height;
Eph 3:19 And to know the love of Christ, which passeth knowledge,
that ye might be filled with all the fulness of God.
Eph 3:20 Now unto him that is able to do exceeding abundantly above all that we ask or think, according to the power that worketh in us,
Eph 3:21 Unto him be glory in the church by Christ Jesus throughout all ages, world without end. Amen.
Jesus said it like this concerning the gift of the spirit:
Joh 14:21 He that hath my commandments, and keepeth them, he it is that loveth me: and he that loveth me shall be loved of my Father, and I will love him, and will manifest myself to him.
Joh 14:22 Judas saith unto him, not Iscariot, Lord, how is it that thou wilt manifest thyself unto us, and not unto the world?
Joh 14:23 Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him,
and we will come unto him, and make our abode with him.
Joh 14:24 He that loveth me not keepeth not my sayings: and the word which ye hear is not mine, but the Father's which sent me.
Notice the same language that John who wrote this Gospel used as seen above in his letter.
Sin is destroyed and the work of the Devil destroyed when by faith we receive the fullness of God. Greater is he that is in you than he who is in the world.
Col 1:27 To whom God would make known what is the riches of the glory of this mystery among the Gentiles; which is Christ in you, the hope of glory:
Gal 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
blessings.