Of course, to have some form of credibility, it's best to have actually read/watched/played/listened/joined/followed to some of the hated work, but some people usually hate without having any knowledge or something parroted to them by another hater.
If you hate the fans of a fandom, that makes you a Fan Hater.
A Fan Hater does not have to be part of a Hatedom.
Anti-Fans of a work are likely to view its fandom as a Fan Dumb.
Fans of a work are likely to view its Hatedom as a Hate Dumb.