Ok, I'm gonna be REAL controversial for a second:
Saying "incest and underage fics are ok because it's usually CSA survivors recontextualizing/processing their own experience" is just purity culture lite. It's like saying "Birth control should be legal because some people use it for non-birth control related purposes" or "abortion needs to be legal because women can die without it."
Yes, these are TRUE and IMPORTANT things. But kind of... not the point?
Kind of giving way to the antis, the puritanical right, the misogynists who just want to control women (because you KNOW they aren't thinking about trans men or nonbinary people when they legislate abortion).
Lemme see if I can explain: by saying "look at this VALID and IMPORTANT reason someone might have for doing the thing you don't like," you are saying that there are invalid reasons for it. That some people shouldn't do it.
You are saying that it is objectively wrong, and that exceptions must be made for it to be okay. And putting aside the fact that NO ONE should have to disclose their personal trauma for judgement, that no one should have to disclose their personal medical history to a judge or legislator before receiving treatment... you are conceding the point.
I refuse to concede anything on this.
I like fucked up fic, I like being able to fuck without getting pregnant, I like that if my birth control fails I can still make a choice about whether or not I want to be pregnant and give birth. I WILL NOT go into my reasons on ANY of this. Because YOU do not have a right to that information, and I am also protecting the privacy of everyone else who does not want to share their reasons.