I think people hate "emo" kids for the same reason people dislike cheerleaders, band kids, or "cool"/popular people.
Most "cool" people just look at someones clothes or the people they hang around and think that they look weird. Then all their friends will of course have to hate that person as well along with his/or her friends so they don't have to lose their popularity with that person in the school. That is why I think most people hate emos. Well that is what it is like in my school. And the band kids or drama kids most likely want to be "cool" so they dislike them too so they don't have to be uncool for liking them.
I personally like emo kids. They all are just so amusing to me. I love how they dress and act around others. Like all my friends get sad and angry a lot but I like being there for them. I like having someone needing me. XD