Here's a few of my ideas on the subject.
Blocking roads is a dick move. You can "protest" in other ways that don't impact other people. If your cause is justified, you will change minds. You don't need to impede other people.
Why is there a need to "protest" this? It sounds like things went as they should - a horrible thing happened, it was investigated and is being dealt with. The officers have been fired and are being charged. Due process is happening. Can we wish the bad thing didn't happen? Sure. But what part are people actually protesting - the system working as it should? It sounds to me that people just want to "protest."
And that leads to this... when have we seen the people "protesting" keep their own in check and it not lead to violence and riots? There's not a good track record here, and that makes the rest of us a tad bit skeptical - justifiably so. George Floyd protests erupted in the "summer of peace" with "firey but mostly peaceful" riots where dozens of people lost their lives and billions of dollars worth of damage.
I'll believe in these "protester's" ability to keep it peaceful when I see it. I won't be holding my breath however.
And lastly, I'm man enough to admit that it tribal at this point. When we see folks from the Left support any effort of the right it'll be the first time. Why would anyone expect side A to support, let alone encourage, side B? That's delusional thinking.