The sad fact of the matter is that a very large number of police officers are simply bullies in uniform. Asserting your rights to them, or acting "uppity," will only get you in trouble.
What you won't see (or will see very, very rarely) is a cop losing his job and standing trial for assault if they wrongfully use physical force on a civilian. They can always get away with "well, I thought he was carrying a weapon" or other such flimsy excuses. Combined with the fact that cops always look after their own, it becomes very difficult to successfully and meaningfully persecute a cop for abusing their authority.
I'd like to believe the world works the way you think it does, experience has taught me otherwise.
[1] http://www.huffingtonpost.com/2013/11/05/david-eckert-enema-...
I think the correct phrase for this situation is, "you can beat the charge, but you can't beat the ride."
Police get all ornery when there's any kind of perceived challenge to their authority.
As a former Los Angeles sheriff's deputy who agrees with the majority of sentiments in this thread, I can confidently say that your broad statement is nonsense. Everyone, not just upper middle class whites, should know and assert their rights in police encounters.