Folks, calm down. This is a case where BOTH sides are right.
First, this is a classic case of "trolling", and one that is almost admirable in it's ingenuity. For one thing, it's very careful NOT to cross several lines. As was pointed out, it doesn't specifically bash fat people -- instead, it bashes a specific form of fetish known as the "feeder". If anything, I can actually get behind that a bit: I believe size acceptance doesn't mean the obsession over increasing the size of oneself or one's partner. But then, people think I'm weird because my lovers tend toward the larger end of the scale to beging with.
The trick is to push people's button's indirectly, in a way that appears casual, yet is cooly calculating. The point is to giggle when the reactionary types shrill out "OFF WITH HIS/HER HEAD!" And make snarky comments about deleting the post. In this, he (or she... on the internet, no one knows you're a dog) can sit back and egg on the attackers by demanding that they be told exactly how they were disobeying the rules. Or they can just sit back and giggle maniacally as they whap off at other people's misfortunes, forgetting for awhile that they might be thin, but they STILL can't get dates on a friday night in the Castro on Halloween.
Your only defense? Ignore them. They do get bored and go away. Or they cross a line trying to get a response, and then you can truly trot out the rightious indignation as you delete their sorry ass.
But this is only the humble opinion of a veteran of the 'Net (or 'Nets, if your a Lush/Cheater supporter) since 1978. I could be wrong.