A refresher, if you encounter someone who tries to use the "fire in a crowded theater" doctrine to try to argue away the First Amendment:

The line, often quoted by censorship advocates, is from a 1919 Supreme Court opinion (Schenck v. US) by Justice Oliver Wendell Holmes. It de facto outlawed trolling.

It was later overturned in a 1969 case (Brandenberg v. Ohio), which severely limited the situations in which speech becomes actionable. It added litmus tests like "imminent", and "likelihood".

The "fire in a crowded theater" argument is not only NOT a law (it came from the judicial branch, not the legislative one), it's not even CASE LAW. It's nothing. A historical note. An error by the Supreme Court that they corrected 50 years later.

The First Amendment is part of the US Constitution. It is the very first change made to the Constitution, once they realized that the government needed to be explicitly constrained from infringing on human natural rights. It is the law of the land. Do not believe a misinformed (or politically biased) authoritarian who thinks a Constitutional amendment can be overruled by a erroneous deprecated court paper.