On Monday the U.S. Supreme Court ruled that the state of Illinois violated the First Amendment when it forced home-care workers who receive government stipends to pay union dues to the Service Employees International Union. Writing for the 5-4 majority in Harris v. Quinn, Justice Samuel Alito ruled that the state exceeded its lawful authority by treating such workers as government employees “solely for the purpose of unionization and the collection of an agency fee.” “If we accepted Illinois’ argument,” Alito explained, “we would approve an unprecedented violation of the bedrock principle that, except perhaps in the rarest of circumstances,...