The American police system is fucked up beyond belief. It doesn't matter whether individual police officers are good people or not, the system itself is deeply flawed. And I'm honestly not sure who or what to blame.
Anarchists blame the mere existence of police. In their eyes, we shouldn't have police forces at all. Needless to say, I don't find that realistic in the slightest. I'm not opposed to the very concept of law enforcement.
Socialists blame capitalism, claiming that the only purpose of police in a capitalist society is to defend the financial interests of the upper class. But I really don't find this view to be credible. Most of the developed world is capitalist, yet police brutality and abuse aren't nearly as prevalent in other democratic first-world nations. The rate of citizens killed by police in the U.S. is an order of magnitude higher than it is in most European nations.
Progressives blame racism. That's certainly part of the problem - a very large part of the problem in some areas of the country - but it's not the core issue. Israel is a far more racist country than the United States: Palestinians are literally second-class citizens with limited civil rights, and they're treated far worse than any American minority group, yet our White citizens get killed by police at a higher rate than Israel's Arab citizens.
Libertarians blame the militarisation of local police forces. Again, I think this is a part of the problem, but only a part. And I also get the feeling that police militarisation is, in itself, a symptom of an even larger problem.
Some liberals, inexplicably, blame civilian gun ownership. This is utterly baffling to me and I don't even get how or why anyone could believe it. The argument that stronger gun laws will prevent police violence seems completely backwards to me.
More than anything else, I think the problem has to do with the culture of law enforcement in this country. Police are trained to act more like a foreign occupation force than a part of the community, especially in poorer neighbourhoods. They're trained to constantly look for threats and deal with them as ruthlessly and efficiently as possible. They're trained to stay detached from the populace, to view citizens with suspicion, to treat everyone as a potential threat. They're trained to defend each other at the expense of everyone else. And until we change the culture of policing in this country, these problems are only going to get worse.