Who wants to hang out in Ferguson tonite
If you want a real answer to why people act like this then get in line. Sociologist and criminologist have spent decades trying to figure out why people commit crimes. There is no answer but some people believe in theories.
If you are really interested in this just do a quick google search on collective behavior. A lot of professionals try to make it more complex then I think it really is.
I can't remember his name but there was a French sociologist who believed the group mentality takes over. People feel anonymous and think they can get away with a lot more when they are involved in a riot.
Now if you ask me what causes the initial burst of violence then I have no clue. That question is probably better suited for a psychologist.