Meh. I don't get it either, but whatever. If their weird social and sexual deviations make them happy, then, by all means, let those people do what they want. I honestly don't see how it's different from BDSM. As for the social isolation, that happens with a lot of other groups, anyway. As long as they don't force other people into it, it's their right.
If I do have a complaint about bronies, however, is how they cry and whine about how everyone hates them for no reason, and how nobody understands them, apart from the shit fits they burst on when called "bronies" and whatnot... BUT, when someone says "You watch MLP? Are you gay or something?" then they all respond "WHA?! NO! WE HATE FAGGOTS!!!". Ah, the hypocrisy.