...anyways
I think Spider is right about dumbs being dumbs, however I agree with Saz and Comrade about it being due to ill-treatment. I also agree that it is absolutely necessary for real change.
Any real political movement requires a fringe. Things work out best when a movement is like 85-90% moderate, and 10-15% radical. Assuming the usual intelligence quotients apply, you're looking at 5-7% of any good movement acting aggressively and irrationally. That's a good thing. Human beings are part rational and mostly irrational, so it balances things out when a movement is part irrational and mostly rational. Without angry black Americans doing sometimes shitty things, slavery and segregation and police brutality will just keep on going more or less forever. It takes a paradigm shift to move society on issues like this, and that means, every now and again, the tree of liberty gets watered with some blood.