I don't completely agree. While killing rampages could qualify as hatefics, I don't think this is the case every single time. Same goes for adult material. I feel the line between hatefic and darkfic/adultfic are blurred and at times it's hard to tell what's a true hatefic and what isn't.
To me, a hatefic spends more time bashing the show, but even then this can be hard to pick out at times. There was a hatefic I read once about Digimon, and the author there did show it was a hatefic, definitely.
But I cannot say the same about Cupcakes. While it does involve Pinkie Pie killing ponies and being out of character, that alone doesn't make it a true hatefic in my eyes. All it is to me is a very grimdark fanfic. The author may have been interested in writing such a story simply because they wanted to, not because they hated the show or Pinkie Pie.
But that's just my view. I'm not saying I like Cupcakes. I already stated I don't. All I am saying is that I don't regard it as a hatefic simply for being very violent and OOC. I don't recommend reading the fanfic to anyone, but if you are curious, you can find it on Equestria Daily, where it currently garners around 900+ four stars out of five rating. Oh and that's another reason I don't think it's a hatefic, as I don't think a hatefic would have such a high rating on a MLP fan site.
Anyway, onto another topic, MLP related. I'm looking forward to season two. If anyone follows Equestria Daily, you might have seen the supposed script of the first season two ep. I'm not sure if it's real or not, but if it is, it'll be an interesting episode. Someone already made an interpretation for Discord. I wonder what he'll really be like.