They are ignorant and hate on the previous generations of MLP any chance they can get. They think that G4 ponies are the main focus of the franchise.
Not all of us.
However, the ones that do, are very annoying (and there's a few other things I don't like about the brony fandom, despite being part of it).
From what I've seen, the arena is fine with the brony fandom - when it behaves itself. This is a very nice place, so it wouldn't hate on every brony, just the bad ones (I think).