Are you saying that they are sinless perfectionists?
Please stop jumping to this straw-man, nobody is talking about sinless perfection.......
There was only one person who tried to pass this doctrine off on here and he got banned a long time ago.
Apostle John is talking about how true believers will walk compared to false believers, and he clearly shows like Paul did if you walk in a hateful and unforgiving way then the Love of God is not in us. Thus he also says the Truth and eternal life also is not in us.
When we are walking properly in the faith (walking in the Light) then we will have these traits about us:
We will be loving, caring, compassionate, show mercy, be longsuffering, have self-control, and obedience to the Lord....
Will we mess up from time to time, yes, but that struggling or stumbling does not excuse deliberate continuous behavior which is what John is talking about.
When he said are sins are forgiven it is because he is talking as Paul did, to believers who should be walking in those conditions mentioned in the fruit of the Holy Spirit !!!
When walking by the Spirit that fruit will in no way lead one to transgress the moral law of God !!!
(Which is also called transgressing against God)