If you wanted to see the truth you could find the answer in that post. If you don't want to see the truth then why did you even ask the question? Something doesn't have to be harmful to be sin. All sex outside of marriage is sin.
you said: Something doesn't have to be harmful to be sin.
If I was not seeking truth I would ignore logic and evidence. I would make pronouncements like 'if you were seeking the truth you would find it in what I said" and not even try to address legitimate logical questions.
Then the answer is that there is no harm to consensual sex?
