Because when people see black they instantly see the stereotype of bands. If there's black they're dark, depressing and instantly stupid and emo. I don't even know why they say it's emo. Emo's have their own feelings, you know, and they're people too.
You see, the society we live in now is more than just fucked up. The society we live in now is led by stereotypes and first-sight guidance. Is wrong and immature, but we can't do anything to change it. There are very few people who actually try to know some bands before judging them. People actually don't HATE My Chemical Romance, they just don't like it and mistake their feelings for hate. That's another thing the media has done.
Also, is not about Gerard's voice, Frank's guitar, Mikey's glasses or Ray's hair. Is all about looks. You see? Everything is guided by looks, although it shouldn't be like that. You're lucky you don't live on Spain, because that's the mainstream of things. Just belive in what you think is right. In what is ACTUALLY right. Don't guide yourself by looks, actually get to know them.
Peace out, hope you find this useful.