A few years ago a Hispanic was stopped for a variety of offenses, DUI, reckless driving (wrecked car for some validity), leaving the scene (at 70+ MPH), etc. When at trial, the attorney said he was stopped due to his ethnicity. This argument was tossed when it was shown that the arresting officer couldn't have seen him because it was dark.
Bingo. This is an important point. Most cops do not stop someone until they see a violation and they see the violation before they ever see who did it. This is because a car can be seen a much greater range than a driver.
This does not mean that profiling does not happen. It simply means that profiling is a much less likely reason for a stop than the simple fact that a driver committed a violation.