The dude I Fux has and editorial on unethical police behavior, including a racist incident that happened to his family in Utah basically for "driving while being brown" (Mexican American & Kurdish).
I think that those that are 100% one side or the other are wrong, eg "Fuck The Police" (NWA) vs "Friends of the police, support the troops" (right wing douche-bags like Sean Hannity).
I have an uncle who is a police. That guy is a standup dude, I'm sure in his town/suburb the community is well served where he happens to be a sheriff.
Basically I think that every situation is unique, and that like for humans in general, for the police there is:
1 a majority of apathetic douche-bags that really don't care about helping the community, it's just a job. OTOH this group isn't genuinely evil either.
2 a minority (maybe 20%) of good-hearted, altruistic cops who are in the police profession to genuinely serve the community.
3 a smaller minority of evil dudes that are sociopaths, and criminals with a badge, such as the officers that continued to savagely beat Rodney King after dude was obviously on the ground & posed no danger to anyone.
I think the show "The Wire" is probably a very accurate representation of real police forces.
Talib Kweli has an interesting take on the police expressed on the track "The Proud" from his excellent 2002 album "Quality"