The Nixon campaign in 1968, and the Nixon White House after that, had two enemies: the antiwar left and black people. You understand what Im saying? We knew we couldnt make it illegal to be either against the war or black, but by getting the public to associate the hippies with marijuana and blacks with heroin, and then criminalizing both heavily, we could disrupt those communities. We could arrest their leaders, raid their homes, break up their meetings, and vilify them night after night on the evening news. Did we know we were lying about the drugs? Of course we did.
Making things illegal and selectively enforcing them is best way to exert control.
Same goes for "Dogs must be on leash" signs. They're never enforced in the park near my house until some undesirables have a small puppy running around.
Same goes for cockfighting. If you're white, you can invite police over and they gamble on the sparring with you. If you brown, you going to prison.