When I was a teacher, we had the saying "It's an explanation, not an excuse" when referring to students' backgrounds in relation to their behaviour. People who are reacting negatively to the violence and rioting in Baltimore need to understand why this is happening. That understanding does not mean that you are excusing it. No, it is neither strategically nor morally correct to respond to police violence with more violence, but if you inform yourself just a little bit, you can begin to understand why it is happening. It is the sadly natural response of a powerless community who has been attacked their entire lives by gangs of well-armed thugs protected by the law.
What would you do if an army came in and dragged a friend of yours away for no reason, broke his back and killed him and there was nothing you could do to even find out why it happened, let alone get justice and prevent it from happening again?