Ta-Neishi Coates, one of the best writers around, has written "Violence does work" which in many cases throughout history is true. However, I think even he would agree violence is more effectively used by those with the power to shape such violence in the manner they wish to choose. This is true in both what violence hopes and the narrative in which it is justified. Those without power can use violence too, but wind up double losers in the process.
The first loss of course is the grievance in which violence arises. The rioters of Baltimore may well have had a good argument to make against abuse by the police force which their taxes (sales or otherwise) support, but said argument is simply negated by destruction of property and theft. Whatever they had to say was lost in the general revulsion to hooliganism (although if you are going to riot make sure you're not trying to make a political point. People seem to be more accepting of sports riots or even riots at the Keene, NH. Pumpkin Fest, for example).
The second loss comes in the aftermath. If violence does have an effect if highlighting grievance, and even if some good comes from it, the damage and scars which come from it take a lot longer to heal. There are probably communities which probably still haven't recovered from the riots of 1960s let alone what may come in Ferguson, Missouri or West Baltimore. As was the case in Detroit, the result violence may have resulted in the transfer of political power from one community to another but only at the cost in human and capital flight leaving those left almost nothing to work with. What justice is obtained becomes ashes as the years.
To give a good example in American history, go back to Shays Rebellion of 1786-87 when debt-ridden western Massachusetts farmers rose up against the state government. The rebellion was put down but one would have hoped their grievances would at least be given consideration. Some of them were (taxes were reduced and there was a moratorium put on debt collections. But the upshot of the rebellion was a U.S. Constitution approved and ratified which created a bigger, more powerful government than the Anti-Federalists would have dreamt possible and the establishment of that day closed ranks (the rebellion prompted Washington to come out of retirement and chair the Constitutional Convention) to create a government to deal with future Shaysites. Again violence by the less powerful led to a double-loss. Perhaps its why the Gandhis and Martin Luther Kings of the world thought non-violence not just morally superior but better tactically too.