That corruption definitely trickles down through the ranks, which is how you end up with brutal officers who think the people they're meant to serve are actually the enemy. I think these folks are trapped in an impossible position and try easing that dissonance through...
...drugs and alcohol, misplaced anger, a sense of entitlement and being the victim whenever there's pushback. Any job that forces you to stare at people on their worst days all the time will take its toll.
It might be a weird take, but I think police need more emotional support