I am so tired of seeing this overplayed urban myth. The precedent you mention was set by Schenck v. United States in 1919, but it was partially overturned later in Brandenburg v. Ohio in 1969 [0]. Which is the part that people who bring up this myth every time conveniently forget about.
So no, you can yell "fire" in a crowded theater or whatever else you want, as long as it doesn't meet the legal standard for imminent lawless action (e.g., a riot). And the legal standard for imminent lawless action is much higher than you think it is.
> as long as it doesn't meet the legal standard for imminent lawless action
So there is no absolute free speech then. Which is the point of bringing up the "fire" example.
If you're a visitor in my house there is no free speech at all. If you say something I don't like I'll legally kick you out. Private companies such as Twitter and Facebook have the same right. Their platform, their rules.
If someone is a visitor in your house, you can kick them out for literally any reason you want or no reason at all.
No idea how this is relevant to your claim that "yelling fire in a crowded theater isn't allowed under free speech". It is legally allowed under free speech, it isn't a crime, despite what a lot of people claim. The theater might kick you out or ban you, but that has nothing to do with free speech.
The other part of the myth people forget is that the metaphorical fire-yellers were socialists distributing anti-draft pamphlets. It's hardly a good thing to cite today on freedom of speech.
Also disagree that such unrestricted free speech is constructive or beneficial. Sacha Baron Cohen explains it best: https://www.youtube.com/watch?v=ymaWq5yZIYM