I think the thing with cops is simple; they're people and like all people, some are good and some are bad. That police in some parts of the world seem to attract a lot of bad guys is probably true, I don't think it's fair to paint cops in general to be over aggressive bad guys. It's obviously a very stressful job and in some situations you decide to er on the safe side and use too much force. In the video being discussed here I think that's very obvious. Punching this girl in the face while she is unarmed and already down is excessive. I doubt anyone in this topic disagrees with that. I do have some sympathy for cops in general since, as the general public, it's very easy to decide someone is an aggressive psychopath over a 20 second video. Perhaps the guy has been shot at by a harmless looking victim before, perhaps there are other factors that lead to this. I would never want to be a cop for these reasons obviously, I'm not brave enough to go after bad guys and probably wouldn't be able to correctly assess all these situations either. You can reason that if a cop can't do this either, he shouldn't be a cop, but that's very easy to say from the sidelines.
Cops are people and some people are cnuts. That's basically how it works. I don't think there's some institutional country wide master plan to keep the little man down with violence.
I've actually had a bad run in with two cops on new years eve. I was drunkly cycling home with a friend sitting on the back off my bike when we were pulled over. The cops shouted, face against the wall and don't say anything. I proceeded to, admittedly in a snarky way, tell them that's ridiculous and wanted to know what I did wrong. They proceeded to tackle me, cuff me, and haul me off to the station where I spend a night in jail. Hardly seems fair, but after an entire night off chasing after aggressive drunk people they were probably weary and had reached the end of their patience. I was mad about it, but the bed in my cell was comfy and I never bothered to make anything out of it.
TL;DR:
uhm, some cops suck, but context is important. The incident in this topic is an obvious case of excessive force though.