@butwhy,
Sigh, I feel as I'm opening a can of worms and am not sure if it is worth starting a discussion on this topic; but I do feel a reply is necessary.
Instead of trying to refute your viewpoints, I think the issue is a matter of perspective.
Several Westerners will say the exact same thing about Pakistanis, Arabs, and Muslims. You can take both of your comments and instead of Africans replace it with Pakistanis. "Pakistanis are barbaric idiots who have incestuous relationships (marry their first cousins), throw acid, and feel that the best way to resolve any dispute is to blow themselves up. Nothing good has ever come out of Pakistan. They should all be wiped out (or some variation thereof)"
Do you think that's fair? How would you refute those statements? Why do you think those criticisms are unfair but valid for black people in general?
Could those same refutations not be applied to people of African descent?
I would simply point out that a lot of problems arise from poverty: it dictates a society's mentality and mode of thought. Furthermore in the US (where these pictures are from), there is an enormous amount of institutional racism. The very nature of society embeds within you the notion that you are inferior, for no reason other than the color of your skin. And that is the frustration and anger you see spilling over.
What you're not seeing are pictures of black people cleaning up after these idiots. You're not seeing black people standing up against rioters (there's a difference between rioters and protestors). Heck there's an article floating around of how a mother saw her teenager on the news rioting and vandalizing, and went there and smacked some sense into him.
Don't judge an entire group of people based on no information. Or if you want to (that's your prerogative), then at least be willing to be judged in the same derogatory and insulting fashion by Westerners, Indians, and others.
There are anthropological reasons for this behavior, there are several economic and political reasons for African economies struggling (quite a few African nations boast a higher GDP per capita than Pakistan, Syechelles (7x more than us), Equatorial Guniea, Bagon, Maruitius, Namibia, Angola, Swaziland. Many places have a higher standard of living than Pakistan.)...if you want I can go into them. But I do think your disdain towards this entire group of people is very unfair.
