Most incest happening in the world is not done between consenting adults. It is done through rape of children. Leaving that out may be construed as a way to shift of the overton window on incest.
You can, of course, point to reliable statistics on that, collected and analyzed using defensible methods. Right?
I suspect that you are wrong, and that most incest happens between same-age adolescent or young adult siblings (and even more between cousins if you count cousins). But I don't have any actual data to back that up either, and would be amazed if any worthwhile data even exist.
Let me make sure I got this right... I make a statement about how a lot of incest is due to rape. You cannot fathom that and ask for stats. I provide them from a child abuse organization that also links to the underlying government statistics. You respond with it's irrelevant. You are not arguing in good faith.
Even "a lot" could reasonably be treated as having been a statement about the proportion, but it would not have been a precise enough statement to argue about. And "a lot" could also be treated as talking about an absolute number, in which case the question of whether something was "a lot" would be a total matter of personal opinion.
"Most", on the other hand, has a very clear meaning in terms of relative numbers... which that RAINN link does nothing to support.
"Arguing in good faith" includes not trying to quietly rewrite your position in the middle.