Earlier quoted context omitted.
The restrictions on speech in the US are confined to “imminent lawless action”, per Brandenburg v Ohio. I think the commenter to whom you are replying might be entirely fine with Reddit’s speech policy following that precedent. And no, shouting “fire!” in a crowded theater is not illegal and is protected by the First Amendment.
But you can't shout fire in crowed theater with the intent to cause chaos. You can shout fire in a crowded theater, if there is an actual fire.
https://www.theatlantic.com/national/archive/2012/11/its-tim...