Unfortunately, Hollywood isn't as good at genre definitions and the like as this forum is. It seems like some people just don't know the differences between horror, gorn, dark, and thriller genres sometimes, and will just throw stuff over the lines as a cheap substitute (I'm all for genre-bending, but it must be done with grace)
Cupcakes is senseless violence, but the fact that its intent is non-seriousness and aimed at humor is why I find it funny. Violence needs a point or purpose, even if it's so tiny or significant. I don't mind violence or gore in the least, so long as it has a purpose. All of the violent conflict in my fic and ones I read maintain obvious cause and effect. I hear a lot about Slendermane and Rainbow Factory for horror, though you almost never hear about Slendermane now--just like Past Sins. :\
Personally, I'm allright with fan stuff. Actually, I kinda like it. Okay sure, you got the clopfics and badly written gore fics, but then you can find pretty decent fanfics out there, whether they stick close to the show's tone or not. As for darkfics, I think that they can be pulled off successfully, it's just that they just arn't always pulled off successfully. I'm actully working on a fanfic that'll get pretty dark at times, and it does change a couple things about the show, but I'm trying to have a decent amount of humor in it as well. Oh, and it involves zombies. I'm actually one of the bronies who loves shipping, mainly because it's kinda cute IMO. I respect the opinions of those who don't like it though. Everyone feels diffrently about that kind of stuff, and if you don't like shipping, then that's fine with me.