I don't think they should go into the Fiction center. Fiction, to me, is a novel, a story with a beginning, middle, and end. Conspiracy books, as well as other subjective beliefs, aren't "stories". And if you start splitting hairs about subjective beliefs not being nonfiction, then you're going to eliminate a lot of it because you'll have to start getting into religion, health, and even some history (Holocaust deniers!). I think it would be too much to start to be "politically correct" about the topics, so lumping it all together is much easier than coming up with a whole new system.