My theory on why the police need to use some level of brutality is because a mob mentality is an animal. It's an amorphous mammalian manifestation that is afraid of loud noises, pain, and losing it's ability to breath easily. So they use counterpart tools to control it, because when this animal cant be controlled, the whole city could be be razed in flames. (As an example, https://en.wikipedia.org/wiki/1992_Los_Angeles_riots#Destruc... )
Im not excusing shitty behavior, but it's worth considering there are millions of events going on in these protests, and all the excess force ones fit in a bullet list on my monitor. Also, in many of the listed events, the cops told people to move away or go back inside repeatedly before taking action. From their perspective, keeping battle formation is necessary to success. And lawfully, you are supposed to comply with this demand.
Just things to consider. I hope I'm not gut-reaction-down voted for taking the middle ground.
They are in an incredibly difficult situation, and putting their lives at risk. I think there are plenty of cops who care about their community, but they do what they have to do because there is no efficient way to communicate to or painlessly control an emotional mob of people (plus bad actors climbing out of the woodwork to cause harm to the community). When you talk to a mob, you aren't talking to anyone.