I think there's a bit of a chicken/egg situation too. Seems like everyone keeps complaining about the corrupt police force, which I get because they are doing some pretty unscrupulous things, but honestly would you strive to do your job well knowing the people you worked for hated you?
I have sympathy for police in modern America. They need to quickly get their asses in check, but I can see how easy it would be for them not really give a **** about their communities with their precedent and the prejudice held against them.