Protestors

I get that protesting is an American right, but why do people have to do it every time something happens that they don't like, it's not like protesting is going to change it. With all these cops not getting indicting for their crimes, I have a funny feeling that these protests aren't going to be as peacefull as they are now. With what happen in Ferguson, you might wonder what if it happened in New York City. Yes, there was protest at Time Square, but that was very peaceful, nothing got burned down. The big question is though, what if they is a riot like Ferguson in New York City. I always wonder what the police would do?