Well, the police forces of America are one of the few remaining places where racists, homophobes etc. can violently exercise their bigotry without punishment.
In a social, business or academic setting, there are repercussions. You can't just lay the beatdown on somebody for their color, religion, gender identity or whatever it is you hate, other citizens will be able to exercise ongoing negative feedback against you even if the law lets you walk.
But cops, they can murder people in cold blood and get away without a day of prison time - and they can take revenge on anyone who doesn't want to let them get away with it. So of course the profession attracts people with these propensities. What was it Diehls said? Something like "by creating a use for men who could exercise brutality without remorse, we not only attracted sadists, we created them?" Something along those lines.
If we held police to higher moral standards than other citizens - rather than lower - perhaps this could be reversed. But right now the system encourages it.