The police that do this and turn a blind eye to this cause these problems.
The first few minutes were standard police brutality, showing the guy who's boss and ensuring compliance. At the same time, they were antagonizing and taunting him to "get up and get in the car" while keeping him pinned. It seemed like a game to them. For about the last few minutes, the cop was pressing his knee into the neck of an unconscious, motionless, dying man. Dude was cuffed and effectively dead and the cop was still pressing his knee into his neck. And none of the other 3 cops did a thing to stop it.