I'd wager it's at least partly to do with seeing the - pretty, privileged, somewhat innocent and boyish - "hero" defiled. I think there's usually a character in every fandom who gets to fulfil this role - and who else would it be in JS&MN?? - Norrell is too repressed, Childermass is way too knowing, Lascelles too evil, Drawlight reads as a bit of a tart. Etc. Segundus is probably next-in-line, but he comes across as rather timid, so it's less satisfying to take him down.

(And where there's hurt, comfort is usually close behind...)