What makes abuse from police specially wretched it that the Law affords you no consideration or legal protection in defending yourself from it. You are obligated to sit there and take it. Even running away or otherwise avoiding his use of force opens legal grounds for him to exert even more force on you. You will always be guilty, even if he hurts his fist on your nose. So when a cop decides he wants to hurt you, there is nothing you can legally do to stop it.
To make things worse, impunity is the rule of the day. Cops will conspire with other cops to keep them out of trouble. That's a fact. If it's not caught on tape, there will be no punishment. Even if it is caught on tape, punishment is guaranteed to be less severe than it would be for any ordinary citizen. Why are police so adverse to people documenting what they do? Apparently, what they really do is not what most people think they do... and they feel they need to hide it.
We have a situation where you have a culture of we can do as we please attitude and absolute disrespect for those who are not on your "team".. or gang if you want to see it that way.
I believe people in high government like it that way, because it is always handy to have a group of people willing to do your dirty work with no fear of consequences. Post 9/11 (wait, no, longer ago) there has been a steady tendency towards militarization, and centralization of control over police forces. As seen during and after the Occupy Wall street fuss, police agencies have taken on the role of internal security agencies more than just simple law enforcement or community policing.