Deviants want to seek each other out (why else would we all be talking on a porn site?). They have to make themselves known (over and over) until they find others that tolerate them. Once they do, they tend to stick together and form sub-communities in a larger community. They do this for protection, as their behavior is tolerated unquestionably. If you've ever insulted a furry (over anything) online you know how fast another one comes to help out, and how nothing (except for idea theft) seems to be off limits to them.
These sub-communities end up being what I consider the main factor in splitting or ruining a fanbase/website. Because everything Deviants to has to be tolerated, the culture changes and mutates quickly, a bit like cancerous cells in a body. Very soon you get Attention Whores and Obsessors generating content (in this case roleplaying). If anyone takes offense, they respond with "It's just a joke, calm down" and keep going. It quickly stops being a joke when Jokesters get a hold of it, and when Deviants push the limits even further. Also due to the tolerance in the sub-community, most of the fetish stuff happens here under the guise of a joke.
So the short version here is that weirdos group together and tell each other that they're being normal. Because none of them have any sense of appropriateness or restraint, they keep pushing the limits of what they can get away with. Attention Whores with artistic talent end up overshadowing actual artists because the Attention Whore is better at seeking attention The sub-culture mutates because, again, no one can say "hey maybe you're taking this a bit too far." If they do, the response is "It's just a joke, no one actually likes this" even as others respond letting everyone know how hard their dick is. For example,marshmallow flavored pony semen is advertised as a joke even now, despite the fact that most of the people creating it are also masturbating to it.
Now back to the main point. Some of you might say "We usually chase these people away and they get their own board/booru or something, it's not a real problem."
But once the Obsessors have been chased off, we here stop caring. When they come back, it's easier for us to do exactly what I did. "Yeah this fan base is getting too weird. I'm just going to stop going to these comment sections/threads and keep this shit private." And when that happens, the fanbase goes sour.
Of course it's equally possible that, for whatever reason, this never happens. Sorry for the long-ass text. I honestly thought I was alone in this.