I think, the fans who keep defending themselves with the cliché that "bronies are no worse than any other fandom", are missing the point.
Of course everyone knows that, we all were fed up with earlier forced memes, image macros, and certain trends dominating communities, coming from various fandoms. Whenever something is popular, it just fills our corner of the internet.
The people who complain about bronies KNOW that they are exactly like every other fandom: They are complaining about every about fandom through it. About R34, about cosplaying, about fanfiction, about fanspeak, fansites, fan conventions, fanboyism, etc. About the very idea of people being that much... nerdy about something.
MLP is a good way to channel these feelings, because it can also be mocked as being inherently ridiculous even by so-called nerds, while mocking an AAA game's or a sci-fi/fantasy movie's fandom would sound too uncomfortably similar to the mainstream's bullshit about how all escapist fiction is silly childish make-believe.