Sorry simon you are wrong. It happens all the time. Although you might think it can't it can and it does.
That case you mentioned may sound "harsh" but if you take a stroll through many major AA and Hispanic cities you will realizer this happens ALL THE TIME. That one instance was a personal one I was there for however there were countless situations in my neighborhood where this happened. The number of police on the take in areas were there are large AA populations is large. THe reason is because they know very few people will take it seriously.
In regards to complaints... do you really think these people do not complain, yet it gets to a point were they are ignored because of who they are.
Not to mention when we decided to walk to basketball courts or parks in "white" areas we were told to go back. Pulled over and held for no reason then told to go back home. These are things that many minority groups experience daily... it is a violation of thier tights. Period.