The militant side of the civil rights movement was significantly motivated by not knowing how else to make things change. Malcolm X and Dr King had discussions about their diametrically opposed positions on how to move forward and Malcolm basically said that when the peaceful approach doesn't work, the militants would step in and make something happen. Once he came over to more of a moderate side he even offered to MLK Jr to be the "instigator" riling people up so that the government would get on board with King as the lesser of two evils.
The problem with rioting is that it further reinforces people's prejudices in most cases and doesn't help the rioter grow. Instead of rioting, we need to all get together and talk honestly and openly and passionately - leaving bitterness at the door. I think most of us would be surprised to find that "the other side" is a lot like us with similar desires and fears about life. If we took the time to listen to one another then there wouldn't be the need to scream out in the universal language - violence.