Say that there is someone who doesn't like black people, Muslims, Jews and so on, so much so that he or she does want to make false accusations about them to the police. Shouldn't the police know who that person is?
"Mr. White, you have made a lot of phone calls this week about black people. Do you need to talk to someone about how you feel about black people?"
Most people will stop calling after that. Everyone knows what "Do you need to talk to someone about how you feel" means, and nobody likes it.
People who don't stop calling after that should be known to the police, shouldn't they? If they're too afraid to call to say crazy things, what might they do instead?