There is rarely if ever a valid reason for such disorder, unless the state were indeed persecuting certain of its citizens persistently, violently and without cause.
And there, in a nutshell, lies your answer. Some people undoubtedly see it that way, and they might even have half a point. There is a disproportionate number of black people in US prisons, a disproportionate number are arrested, stopped, shot at, killed, etc etc. It's hard to blame people if they turn around and say "no more", and react violently.
On the other hand, some people are just looking for any excuse they can find to loot, pillage and behave like yobs, and certainly that's what's causing much of the rioting. Both in the US currently, and when similar things happened here in the 2011 riots. There were legitimate question marks over the shooting of Mark Duggan (one key difference being that he was actually armed, unless Michael Brown, but in both cases there remain concerns over the official story). Some people took this seriously, and protested the police response. That legitimate protest was then quickly hijacked, and very quickly chaos took over.
Unfortunately, violent people are louder, and so more noticeable, than peaceful protesters. Small wonder that it looks like "certain members of the Black community" find this need to riot. But it's horribly misleading, because two types of behaviour are being mixed together and being made to look like the same when they are just not at all the same in any sense.
And anyway, you could -- and should -- delete the word "black" from that quote above and ask an equally legitimate question: why do "certain members of the community find the need to take to the streets rioting"? Because that's just what some people seem to enjoy. It's nothing to do with skin colour, nor is it necessarily more prevalent among the black community. Doign the rounds of some social media was a list of riots involving mainly white people, provoked by all sorts of "reasons", although they weren't really, including the bizarrely contradictory "losing a hockey game" (2011 Vancouver riot) and "winning a baseball game" (San Francisco 2012; Boston 2004, including one fatality).
Some people are just *** and look for any excuse they can to behave like ***. The apparent excuse is just an excuse, and nothing more than that.