We have the same problems in Canada. It's not just American cops.
Students accuse cops of brutality
Also, Toronto police have a very bad reputation after their behaviour towards peaceful protesters at the G20 global summit last year. They also blocked an entire intersection for 4 or 5 hours straight during this time, mostly filled with innocent bystanders.
Another account of police brutality during the summit:
A second look at G20 police assault - thestar.com
Although I respect the good cops who don't engage in this type of behaviour, it's the bad cops who bully people that make me question that. Some people are just outright bullies, and those are the people who are going to abuse their authority and beat people and whatever if they get hired as a cop.