I think some believe it. Queer Theory in particular seems to attract/prey upon people with Cluster B personality disorders, which are characterized by a lack of a stable sense of identity and persistent feelings of derealization. I don't think most advocates actually believe this stuff, though, because it doesn't make sense, and more importantly, because they don't care that it doesn't; like all totalitarians, they view the world strictly in terms of power dynamics. To them, it doesn't matter whether something is true, just whether something is problematic.