Content-based restrictions undermine the free speech principle. That principle, as the Supreme Court summed up in 1989’s Irwin Toy decision, is that everyone ought to be able to “manifest their thoughts, opinions, beliefs… however unpopular, distasteful or contrary to the mainstream,” because counter-majoritarian speech sometimes turns out to be right, and allowing people to express unpopular views helps us get to the truth and govern ourselves. A great example of the principle in action: same-sex marriage was until recently an unpopular idea, but is is now accepted because we were free to discuss it.