As for the rioting, I think it is actually appropriate.
I see a riot as similar in nature to a strike. In both cases, they are acts of defiance against an authority that is absolute in its ability to impose conditions and actively design the context of negotiation and peaceful recourse, but still depends on the cooperation of its subjects in order to remain an authority.
A business can absolutely refuse to negotiate working conditions and there is nothing workers can do about that. But workers can refuse to work, and there is aboslutely nothing a business can do about that. If the business wants to exist, it can thereby be forced to negotiate with its workers.
Similarly, a legal establishment that wishes to impose order on a population can absolutely refuse to negotiate the conditions of that order, and even in a democracy can manipulate those conditions such that there is nothing that population can do about it (for example by disproportionately turning black people into felons with no right to vote). But if that population refuses to behave orderly, then that order will not exist, and there is nothing the law can do about that. It can thereby be forced to negotiate with its population.
Another effect of both strikes and riots is that it forces indifferent bystanders into the equation. Random comfortably middle-class white guy may not care about how much a fast food worker gets paid, or about the grueling shifts of medical workers. But he does care if nobody is willing to serve him fast food or tend to his illness (a strike can harm innocent people too...). He is more likely then to put pressure on businesses to treat their workers fairly, so they'll go back to providing the services he wants.
Similarly, random comfortable middle-class white guy may not care that unarmed black teenagers are murdered in the street by police. But he is forced to care if every time it happens, his car gets set on fire. He's more likely then to put pressure on police to stop behaving in ways that result in his car getting set on fire.
This ruling yesterday sent a very clear message. That if you fail to immediately and completely comply with any order by a police officer, even one as insignificant as "get on the sidewalk", that the officer can kill you for it and expect no repercussions. And given the well-established racist nature of law enforcement around St Louis, and many other parts of the country, it is clear that the law has the intention and ability to operate as the enemy of a majority black population.
As far as I'm aware, all reasonable responses to this situation have been attempted and met with violent suppression or otherwise failed. Given this, I don't feel that a riot is an inappropriate response.
And yeah... peaceful demonstration has never been the sole component of any successful movement against an oppressive entity.
There were a lot of riots during the civil rights movement era. MLK's non-violent leadership was not solely responsible for its success, and the guy wasn't even non-violent through the entirety of his activist career. The non-violent approach wasn't even his idea.
Another guy went to great lengths to convince him to put down his guns.“What is going on here is real simple,” said DeAndre Rogers Austin, 18, who was with his two younger sisters. “We told them no justice, no peace. We didn’t get our justice, so they don’t get their peace. We’re fucking shit up over here. Plain and simple.”