You're right, there are a few cops out there who out bad behavior. They are punished, demoted, fired, and even confined to insane asylums by the cops they "betrayed". http://www.nytimes.com/2012/03/16/nyregion/officer-adrian-sc...

These cops are the true heroes. Unfortunately the reason we rarely hear about them is that there are incredibly few. Much more comfortable to stick with the herd, follow orders and take your check.