Taboos around violence for political are one of the crucial building blocks for a functioning democracy. If those taboos are broken, even for a good cause, you set a precedence that violence works. And the next cause won’t be as good. One only has to look at the lessons of the Roman Revolution that started with the murder of Grachus, and ended with an Emperor who everyone acclaimed as they were so tired of the bloodshed.
The non-violent protests of Colin Kaepernick were mocked and used to rally the other side and just weren't effective.
The problem here is not the violence, but a policing system that is so fundamentally damaged and has not been effectively reformed fast enough.
The MLK quote is trotted out pretty often, but "a riot is the language of the unheard".
MLK Jr was unequivocally non-violent. That quote was in the context of explaining the root cause of the rioting, not condoning or endorsing it.
Don't trust anyone trying to tell you MLK Jr would have supported violent protests.
They are either trying to manipulate you or sadly ignorant (or both, of course). In either case they have it wrong, in terms of history and in the implication that violent protest will lead to any kind of progress or justice.