After living in Europe for six years now, my wife is still puzzled sometimes by the differences between Europe and North-America when it comes to the police: how they are experienced by the population and how they see and present themselves and which role they think they're playing in society. Big difference. I'm certainly over-generalizing but here, we see cops as approachable and helpful in general (with exceptions) while in North-America, at least my wife's impression is that of cops being mostly intimidating (again, with exceptions).
Of course, this is all complex and different social and societal aspects play a big role, such as e.g., the odds for a cop of running into an armed person. But when I read how the police handled the situation with the group of black trick-or-treaters, it seems so foreign to me now from a more European perspective.
I suppose accountability is always going to be an issue - who watches the watchmen? But it should not be - in a democracy especially, there should be functioning mechanism to prevent abuse of power, and that of course applies to police actions, too.
Simple reason being, that random police violence just results, ultimately, in the kind of uproar and civil unrest the US experience now. Basically the last thing dictatorships want.
Outside of big cities it gets even more lax. You just see police officers hanging out like regular people. I once saw an old guy get into an argument with the cops that looked like an argument between two people, not between "officer and civilian". In the US that wouldn't happen, the officer would feel slighted and probably arrest that guy, or the guy would never dare to talk back to a police officer in the first place.
But to your point I suspect the military police is very brutal.