Unfortunatly for your "theory" John uses the pronouns of "we" and "us" not "they", in which he includes contextually himself, as one who walks in the light, and is cleansed of sin.
He also used the word "IF".
"IF" we walk in darkness, juxtaposed with "IF" we walk in the light.
The outcome of each walk is very different.
You have deceitfully changed the pronoun to "they".
But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin. If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. 1 John 1:7-9
The very same ones (John and the Christians he is writing to) who walk in the light as He is in the light, are the same ones who are cleansed from sin, and are the very same ones who have sin (which dwells in our flesh, warring against the Spirit within our inner man) and must learn to walk according to the Spirit.
Of course if we should sin, we can confess our sin and He is faithful to forgive and cleanse us from all unrighteousness.
You seem to be unaware of these scriptures that, hopefully, will shake you from such an abysmal belief as sin dwelling in your skin and bones.
It is written...
Col 2:9-11,13..."For in him dwelleth all the fulness of the Godhead bodily.
10 And ye are complete in him, which is the head of all principality and power:
11 In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ:
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;"
Col 3:9-10..."Lie not one to another, seeing that ye have put off the old man with his deeds;
10 And have put on the new man, which is renewed in knowledge after the image of him that created him:"
Ephesians 1:7..."In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace;"
Eph 1:22-23..."And hath put all things under his feet, and gave him to be the head over all things to the church,
23 Which is his body, the fulness of him that filleth all in all."
Eph 2:5-6..."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:"
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 4:6..."One God and Father of all, who is above all, and through all, and in you all."
Eph 4:22-24..."That ye put off concerning the former conversation the old man, which is corrupt according to the deceitful lusts;
23 And be renewed in the spirit of your mind;
24 And that ye put on the new man, which after God is created in righteousness and true holiness."
Eph 5:8..."For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light:"
Eph 5:26-27..."That he might sanctify and cleanse it with the washing of water by the word,
27 That he might present it to himself a glorious church, not having spot, or wrinkle, or any such thing; but that it should be holy and without blemish."
Eph 5:30-32..."For we are members of his body, of his flesh, and of his bones.
31 For this cause shall a man leave his father and mother, and shall be joined unto his wife, and they two shall be one flesh.
32 This is a great mystery: but I speak concerning Christ and the church."
Gal 3:27..."For as many of you as have been baptized into Christ have put on Christ."
Not one of those scriptures even hints at something nefarious lurking in the body of the new creature.