People tend to cite the “fire in a crowded theater” quote for two reasons, both bolstered by Holmes’ fame. First, they trot out the Holmes quote for the proposition that not all speech is protected by the First Amendment. But this is not in dispute. Saying it is not an apt or persuasive argument for the proposition that some particular speech is unprotected, any more than saying “well, some speech is protected by the First Amendment” is a persuasive argument to the contrary. Second, people tend to cite Holmes to imply that there is some undisclosed legal authority showing that the speech they are criticizing is not protected by the First Amendment. This is dishonest at worst and unconvincing at best. If you have a pertinent case showing that particular speech falls outside the First Amendment, you don’t have to rely on a 90-year-old rhetorical flourish to support your argument.

Source: Three Generations of a Hackneyed Apologia for Censorship Are Enough | Popehat