You can explain away the plainly written word if you wish:
If WE(John is including himself in the we) claim to be without sin we deceive ourselves, and the truth is not in us
If WE(John is including himself in the we) claim to be without sin we deceive ourselves, and the truth is not in us
Anyway, as I have said elsewhere, the Gentile church doctrine should be from Apostle Paul first and foremost. John, like Peter and James, were writing to their Jewish brothers. (Galatians 2:9)