I really do sympathize with both sides on this.
The vast majority of cops are people just doing a job (and by vast majority, >95%). The problem is, as the Houston example Emo posted earlier, very small numbers of cops can have very large impacts on communities. Throw in the us vs. them mentality that has been instilled in police departments since the beginning of the drug war, improved technology for people to monitor the police with, and you get to where we are now.