I'll just quote from John and leave it at that:
1Jo 1:8 If we say we have no sin, we deceive ourselves, and the truth is not in us.
And John is certainly talking to Christians and about himself as well. The difference between the version of 1 John 3:9 ("he cannot sin") and 1 John 1:8 ("if we say we have no sin") can be found in this verse:
1Ti 5:20 As for those who persist in sin, rebuke them in the presence of all, so that the rest may stand in fear.
Every true Christian still sins but doesn't persist in sin. Every non-Christian doesn't care. If there are tares among the fold who are persisting in sin, then we should call them out simply so that true believers are reminded of the gravity of sin. And we should stand in fear when we sin. Fear not of losing our souls but fear that we should dishonor God and rightfully bring down corrective measures on us. We are His ambassadors and we represent the King. We are to behave accordingly.
Once again you are misusing John’s quote. tHat is obviously meant that all have sinned..not that we cannot be free of it!
No, it is this salvation that John the blessed wrote of..
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