I think the hate threads that annoy me are those that seem to be started for either pointless reasons or to "prove a point" rather than because someone has just got frustrated with one of the people on the show.
The one yesterday about Kelly's underwear line strikes me as in the first category - I mean, there was already at least one "we hate Kelly" type thread, I thought starting a whole new "we hate her" thread just because the girl had a photo-shoot was... well, a bit sad to be honest. I didn't particularly get a lot out of her "day in the life" but didn't think it was any more or less pointless than anyone else's - those things are only really interesting IMO if you actually are a fan of that person to begin with. A bit childish to start a thread basically to throw a strop about it.
Into the latter category I'd put the recent Karen hate thread, which although people can feel free to dislike the woman, to me the first post strongly suggests that the post was posted out of "tit-for-tat" let's annoy other posters-itus rather than because Karen had particularly annoyed someone. Posting a thread largely in an attempt to prove a point/get a rise out of people (and about someone who's no longer even in the competition any more) also strikes me as being rather immature.
That said, I've got to the point where if people want to spend their time posting about how much they dislike someone, I'm going to think it's their problem. (Ditto the few who wonder into fan threads and post about how rubbish someone is, or whatever - my feeling is, "get a life!"). I've done my share of "argh"-ing about contestants in the past but I've decided life is TOO short - I have more interesting things to do.
I can honestly say that, while I don't actively like all the contestants this year, I don't hate or even dislike any of them. Even Kelly, who was annoying me at one point, I now if anything feel sorry for (that's the effect her day-in-the-life had on me, anyway) and my only complaint about her dancing is that I think she is capable of so much better and I want to see it.