I think everyone understands the reality.
The problem is legal immigrants who are US citizens will be subjected to an officer's "suspicions".
Traffic or "Terry" stops are a major tool for police in catching drug dealers and those with outstanding warrants. I personally know cops who will stop someone for a license plate light out and then tell the driver “it must have been a bad connection because it's working now“. So much for "legal contact".
Didn't the country go through this already in deciding to treat all air travelers as terrorists?