Torched buildings and looted stores will win the Dems votes? I doubt that.
By conventional wisdom the Republicans are the law and order party, which would make your statement a good bet in normal circumstances. There are a couple of things going on, however, that I believe make your statement incorrect.
1) the underlying issue is an unchecked police force, which has worked to abuse the black community for generations. Over the past few decades, they have actually gotten away with murder. Monday's killing (lynching) of Floyd was so egregious, so over the top that it has exposed the police as the outlaws. It was 'the last straw". Social justice is a much higher value to millennials than the generations that preceded them. They have been active in the protests. This is likely to motivate much more voter participation on their part than might have happened had things remained calm.
2) the core protest has been reasonably orderly. There are agitators behind the scenes, however. First, there are looters. With 25% unemployment, even much higher in the minority communities, while its not excusable, it is understandable. Much of the unemployed in this group will still be unemployed in November. They will be voting. Second, there are political forces at work fanning the flames. Although we do not yet know who they are, it likely will include anarchists and members of boogaloo, which exist to break down government ... they each are more associated with the radical right than anything.
3) the Republican POTUS, who should be a calming force in all of this, but he has actually served as an agitator. That will win him no votes and cost him many.
We clearly have a very deep seeded race issue in this country, that includes racial and economic inequality. The black community was even harder hit than the rest in the pandemic, which was both a reflection of our poor healthcare system and racial inequality. Trump's policies have worked to make all of these things worse (included telling US police departments that the DoJ would not be investigating them)... any hope Trump had off gaining black votes is gone.