Living in a rural community, it is my experience that law enforcement is bound to a greater degree of accountability due to the lesser degree of anonymity. Larger police forces have greater opportunity for less than honorable members to fall through the cracks and perpetrate offenses against those they are charged with protecting and serving. The blanket accusations against police forces of abuse and overreach are inherently unfair just as any blanket accusation against any group is unfair. The difference is that when an offense is perpetrated by a member of an organization which is supposed to be trustworthy, the individual offense taints the whole of the organization and degrades the trustworthiness of the organization.
I do not believe police brutality runs unchecked throughout cities to the extent of the Rodney King beating and more. These incidents, when they happen, are far more likely to end up on the Internet since everyone carries a smart phone. I also believe these events are generally covered and do not remain a secret for long.
Police brutality in the United States is a relatively rare occurrence, certainly compared with other countries. When it does happen, it usually the result of individual officers acting in clear violation of all established rules, rather that something systematic. Furthermore it always publicized and punished, thus it cannot be said that it runs 'unchecked'.
I think that the idea that police brutality can exist to the extreme levels like that of the Rodney King beating is ridiculous. The fact that there are more cameras around in society is one aspect that I think deters such issues from being a problem. I also think that people like to make these idea more of a problem than they really are for political reasons.
No, I think that police brutality is not unchecked through cities at all, and if you are a victim of police brutality, then you can go to them and tell them, and they will get the cop that assaulted you in trouble, as long as you were not resisting arrest.