First, I'm using "fandom" not so much in the sense of "people who watch the show every week," but more in the sense of "people who invest a lot of time an effort into discussing it / writing fanfiction / posting on internet messageboards about it / etc. etc. etc."
Second, in previous seasons, the fandom's hate was focused on Cameron. Now, it seems to be focused on 13. And to be quite brutally honest, I don't see the reason for the hate. Oh, there's plenty of people who are quick to aver that she's badly written, whiny, incompetent, or just plain sucks. But I think I'd be more willing to take this criticism seriously if it wasn't a carbon copy of fannish criticisms of every other regular female character on the show.
(Which, granted, if you include 13 and Cut-Throat Bitch, that makes... um, four characters during the past five seasons. Which I think might be part of the deeper issue here. And another part of the deeper issue is-- quick, House watchers, can you tell me the real names of 13 and Cut-Throat Bitch? Thank you. And how long did it take you to remember that? And could that be because we don't get their real names too often in the show itself? I think that's a big part of my point, though I might have to work on it some.)
TL;DR: It bothers me how 13 is getting all the hate that Cameron used to, because I think the hate stems not from her actual character, but from some other skeevy stuff instead.