Can a Sincere Christian be an active alcoholic?
Can a Sincere Christian be a repeat adulterer?
If the answer to either of the second two questions is "Yes", then the answer to the first question is likely "Yes"!
Most "sincere Christians" commit some kind of sin on a daily basis, and many "sincere Christians" commit a specific sin on an ongoing basis.
Are they sincere, or not? That is for the Lord to judge, IMHO.
The woman taken in adultery had sinned, and, under Judaic law, was subject to the punishment of stoning (death). Did she ever commit adultery again? We don't know. Did she ever qualify as a sincere Christian? We don't know that either.
According to some, "Once saved, always saved."
Could someone therefore who sincerely became a Christian, yet whose sincerity might have waned, still be a "redeemed" or "saved" Christian?
That is the most important question, of course. I'm glad that making that determination is above my pay grade.
It seems likely that Christ's Heaven might be somewhat more populous than any Heaven whose membership was determined by "sincere Christians"...
I would think the answer is yes- for all the reasons you state in your thought-provoking post #21.
Conflict over this issue occurs when gays want to have their sin removed from the Bible, and order Christians to accept their sin.