This post therefore intends to do two things: explain in greater detail why it is an incorrect statement of law, and also how incorrectly citing it as the law inherently poisons any discussion about regulating online speech by giving the idea of such regulation the appearance of more merit than the Constitution would actually permit. Because if it were true that no one could speak this way, then a lot of the proposed regulation for online speech would tend to make more sense and also raise many fewer constitutional issues, because if it were in fact constitutional to put these sorts of limits on speech, then why not have some of these other proposed limits too.

Source: Why Falsely Claiming It’s Illegal To Shout Fire In A Crowded Theater Distorts Any Conversation About Online Speech | Techdirt