The problem here is that the police are failing to distinguish between groups peacefully protesting and groups who are tearing things up. They're rounding up all the protestors. The police have a responsibility to distinguish targets. Their job is to police, not to suppress. Even in the middle of a peaceful protest they should be making an effort to police the protest by differentiating between people maintaining civil order and people who are not. They should not arrest or attack anyone who is maintaining civil order.
I think the biggest issue with police forces is that they're all basically trained to treat all situations with equal gravity. They fear for their lives even when it is not warranted. And because of that they respond more like a military force, with a level of violence out of all proportion to the situation.
The police are a bigger deterrent to peaceful protest in this country than any politician, and they have been since they came into existence.