No, they don't. They discredit the legitimate point that many state actors wantonly use excessive force in the minds of most Americans. Nobody will listen to proposals while he's worried about his things being destroyed. Nobody is going to vote for reform under the threat of having his business burned or his neighborhood terrorized. Using violence to achieve a political aim is terrorism, and will never achieve long-term social change. All it will do is prompt a backlash and close most Americans' minds to what is otherwise a legitimate grievance.