I have always wondered something about the power of the police and the consequences of enforcing unpopular and or immoral laws.
You are the cop in the late 50's who arrested black bus boycotters and had firemen turn their firehoses on black protestors. You are still alive today and find that your home has burned down. You turn to your community for help. Can the black people you arrested and had hosed legally tell you they will not help you because of what you did back then, especially if you are unapologetic about it? And if the black people who were victims can I am sure whites sympathetic to integration and the protestors could to.
Another question. Whether true or not we have all heard stories about speed traps in small towns. People have gone to jail for putting signs out saying "Speed Trap". However, is there a law saying "Do not like local speed limit laws and getting tickets? Boycott the town's businesses" is not allowed?
Having grown up in a city where such a scenario is possible, I don't it ever worked out that way. If there were consequences for officers who enforced Jim Crow laws, I never saw it. The most likely consequence would be early retirement.
As for speed trap whistleblowers, most of that is urban legend. It's easy to understand why a policeman would be upset if someone exposed their speed trap. However, I've been driving for about 43 years, or so. In that time, I've gotten 6 or 7 speeding tickets. All that I can recall were issued by police officers who were standing beside their car, in plain sight, a short distance from a speed limit sign.
The risk of driving into a clandestine speed trap may be somewhat over rated, but the idea of speed limit enforcement is to encourage people to drive at the posted speed. It's not supposed to be a cat and mouse game where we are free to break the law because there aren't enough policemen to catch everybody.