By way of a general response I just wanted to say that people are way too touchy. Honestly the perverted parodies and such of popular properties are a sign of a healthy fandom in most cases. I read both "Sweet Apple Massacre" and "Cupcakes" to see what the big deal was, despite not being a MLP fan, and it's very similar to literally dozens of other things I've read over the years. Adult MLP fans with a sense of humor should be flattered that someone put in the effort... and I'll be honest in saying "Cupcakes" was actually pretty well written, characterized, and paced, a true classic of this kind of thing. "Sweet Apple Massacre" had more intense concept and sicker acts but wasn't anywhere near as well put together.
In the end nothing should be a sacred cow. This is no differant than the various "Slash books" focusing on homosexual relations between Kirk and Spock (from Star Trek) which was even more contreversial when they were written. Not to mention what Penny Arcade did with "Strawberry Shortcake", albiet without realizing it was a property due for a
relaunch (or so they claim).
To be honest I'm not a writer of fan fiction, but I'm almost tempted to throw my hat into the ring again as an anonymous writer of ultra violent and sexual horror stories and see if I still have the mojo, especially seeing as none of my old stuff I wrote as a teenager is around anymore (I wrote a few semi-infamous text files circulating around BBS systems at one time just for fun).
My only problem with these stories is that they are too easily availible, I think the people hosting them should at least put up a superficial age verification thing. More so for "Sweet Apple Massacre" due to the nature of the sexual content, "Cupcakes" doesn't go much beyond a typical "B" movie and really any kid who has read "Goosebumps" has probably run into similar ideas. Overall what Pinkie Pie is doing isn't much differant than the witch from Hansel and Gretal (whether they survive depends on the version of the story), it's just a bit more explicit about it.