One thing I think people need to try to understand is the greater issue surrounding those beliefs. I think people get offended when its claimed to be racially biased to believe otherwise... In reality I believe these people to be brainwashed. From the moment were born we are told to listen to the cops... When we get our license people exchange techniques on how to get by the cops. Its part of culture to see these guys as all powerful. You see somebody talking back to an officer (justifiable and unfortunately I'm guilty of snapping back at unnecessary nonsense and almost getting hauled away for literally nothing) some people see that and think its the end of the world, when in reality police are not above the law, and we have the right to call them on that when neccasary.
I can definitely see it as brainwashing myself, with some racist beliefs fueling the flames. I think part of it also is that the US hero-fies police work, as if it is the possibility of performing acts of genuine courage that truly is the reason why people want to become cops, and with that line of thinking, well-off Americans (typically white people, but minorities can too) deny that a cop could do anything wrong. In reality, it seems the majority of cops don't really care for "protecting and serving" and more of pushing around people (mostly blacks and other minorities). Go in with the belief you are helping, stay for the feeling of power over those who are "weaker".
I'm a white guy, and my only major run-in with the cops was relatively unpleasant (and yes, my friends and I were completely compliant, and it was over NOTHING). If we were black, or any ethnicity that wasn't white, I think it would have went so much worse. From "colossal dicks" to "potential killers" worse.
Edit: This isn't to say that there aren't racists who defend cops. Of course they exist