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".
You cannot tell a group of people that violence must be beneath them when they're facing a system that employs violence against them with impunity and often bends over backwards to justify it, in a culture which holds violence as one of the foundations of liberty itself. That would be suicidal.
Violence should be a last resort, but it can't ever be off the table, not in the US.