I wish I could tell you the logic behind it, anon, but I don’t understand it myself.
But it very much does seem to be the case that antis love dark, gruesome, problematic fiction, and then want to hold the fandom to be light and fluffy and unproblematic.
I suspect that if you asked any anti, they would say its because the canon isn’t “glorifying” whatever dark material it has, but they somehow just know that the icky fans are “getting off to it”.