"There are a lot of derogatory things said about Twilight, for no reason that I can tell (threatened because it's popular? I don't know)." This.

Definitely seems like the most likely reason for people to attack something they haven't read or seen. I don't know if it's because the fanbase is (as you've said) primarily female, or if other fandoms feel an overlap/toes being stepped on. Neither is justification for trying to make someone feel bad on their vacation.