> And in fact the line from Justice Holmes in Schenck v. United States is “The most stringent protection of free speech would not protect a man in falsely shouting fire in a theatre and causing a panic.” That “falsely” is what’s doing the work, both in Justice Holmes’s hypothetical, and in how such a false shout would be treated by First Amendment law today. Knowingly false statements of fact are often constitutionally unprotected — consider, for instance, libel, fraud, perjury, and false light invasion of privacy. That would presumably apply to knowing falsehoods that cause a panic.
Also see: https://www.law.cornell.edu/uscode/text/18/1038.
That said, this doesn't change your broader point that it seems that most people (myself included) are not very clear on 1A exceptions.