The police are brutal because the civilians are brutal. It's a two way street. Has a Norwegian police officer ever died at the hands of an angry driver? And no, it's not always "cause guns" (though it certainly exacerbates things). In Colorado, a civilian (hunter) killed another civilian with a crossbow on the side of a highway after a fit of road rage. It could have easily been an officer (and indeed officers frequently die at the hands of civilians)
This is the factual context: The number of police feloniously killed each year is under 50 and falling. The number of people killed by police is over 1100 per year and rising, despite overall falling crime rates.
US police have abysmal performance in this. They are brutal, savage, and unprofessional compared to any other developed country. Militarization, the Drug War, and recent political exhortations to be "tougher" do not help.
The US has zero excuse for brutal policing.