I think, as you say, posting anonymously seems to encourage people to leave all common sense behind, and let their nasty sides show. I find it rather astounding that a fictitious world can inspire such venom...I mean, it's just a show, for heaven's sakes!
I personally love the whole show (Buffy), and there are characters I identify with more strongly than others. I would never suggest that because Buffy is my favourite character, all others must love her too...but I guess that's because I'm actually an adult, reasonably able to tell the difference between reality and fiction.