The Watchtower Society's Bible Reference book "Insight on the Scriptures" Volume 2 states on page 971:
Love of God and of neighbour is a principal means for avoiding sin, which is lawlessness, for love is an outstanding quality of God; he made love the foundation of his Law to Israel.(Matt 22:37-40; Rom 13:8-11) In this way Christians can be, not alienated from God, but in joyful union with him and his Son.
(Emphasis added)
So Witnesses are conditioned to believe that the wicked (those alienated from God)really sin. The rest are simply imperfect and are not real sinners.
No wonder then that the Witnesses have introduced the term 'Gross Sin' to their vocabulary, an expression found in scripture just once but found a great deal in Watchtower literature. The Bible reference is to the men of Sodom being gross sinners (Gen 13:13), The NIV renders this "sinning greatly". The Watchtower interpretation, however, leads into the legalistic practices adopted in the elders' judicial procedures where sexual sin has to be categorised and defined. To those not familiar with the elders' manual, the definitions have to do with where, how, and what is touched or carressed the private areas of the body.
Referring back to the above point about the Law in the Insight volume, it should be noted that the Law did not encourage obedience, rather it magnified disobedience. Law merely indicated the sickness, God's love brought about the cure. That is what Romans 13 is highlighting.
The failure to recognise our error, is illustrated in the parable of the Prodigal Son. The virtuous older son complained to his father that all attention was going to the returned prodigal brother. He missed the point of his father's forgiveness. That older son, like the Witnesses, was too busy comparing himself to his sinning brother. He failed to recognise that, he too, was a sinner and benefitted from his father's love. When this parable was discussed in a study article in recent years, it failed to identify this about the son. It stopped short at comparing him, rightly, to the Pharisees. But the application goes much further.
But then, they don't really sin, do they?
Cheers,
Ozzie
"So often, the unpolished
the disjointed
Is on its way to the truth
Ahead of the finished
the polished."
Ken Walsh, Sometimes I Weep