In all fairness, most of it isn't grimdark- the "grimdark" you are thinking of, the shock stuff, is only a tiny fraction of the fiction out there, it just spreads more quickly than other genres because people like to shock themselves and pass along grotesque fiction to their friends. For the most part, it really is rather rare. Anyways, "grimdark" is a horrible term, as it squashes many genres and many shades of darkness in there, and really there is a whole number of genres that get lumped in with shock fiction and promptly suffer from the shock fiction's reputation. As for 1- well, look at the gender ratio, then look again at the gender ratio of the well-developed characters, and you will find that one gender dominates the show, leading to lots of that shipping. I don't see how that is generic or crappy, but your tastes are your tastes. 2- not really most of it, but porn just sort of sits on it's own- I wouldn't really count most of it as 'fanfiction' and 4- well, there is a lot of poorly written stuff, yes, but there is enough well-written stuff to read for quite some time. This community has a massive cast of very gifted writers working in a number of genres. And then there is Sturgeon's Law, which applies far beyond fanfiction but still is worth remembering. http://tvtropes.org/pmwiki/pmwiki.php/Main/SturgeonsLaw However, there is enough fiction in the community to make Sturgeon's Law not as toxic- we have so many talented authors that you can completely avoid the lower quality stuff and still have plenty to read.
Anyways, if you want grimdark, try creating an exorcist-novel like fanfic. Maybe that'll get people's attention.
