WASHINGTON — The Onion has some serious things to say in defense of parody.The satirical site that manages to persuade people to believe the absurd has filed a Supreme Court brief in support of a man who was arrested and prosecuted for making fun of police on social media.“As the globe’s premier parodists, The Onion’s writers also have a self-serving interest in preventing political authorities from imprisoning humorists,” lawyers for the Onion wrote in a brief filed Monday. “This brief …