Personally I am a brony. Just because we like a TV show, does that really make us morally wrong? I don't understand what really makes this even an argument at all. We really like mlp. So what. If you have any complaints, the exit button is right up there. Thank you for your time.
I was at Anime Expo a while back, and the Brony Crowd was the most polite of the crowds there. A lot of the hate towards bronyism, as far as I can tell, is the subject matter. Once you get past that, they could like something like Star Trek and be treated normally.
Also, I looked at the MLP universe. It seems eternally about to fall apart, and they do seem to have a very limited supply of Deus Ex Machinas. I think that the situation will resolve itself quickly enough, for the haters.
The other reason for the hate?
I don't know either, but I have a strange hankering for cupcakes right now.