That was a frustratingly meandering and low-density listen. Here's the substance of the episode, the rest can be discarded:
> Now that we have agreed that not all speech is protected, is this particular speech we are talking about protected? The answer is that first we start with a presumption that a law punishing speech for its content or message or subject matter violates the First Amendment.
> We look to see if the speech falls into a short list of well-defined historical exceptions to the First Amendment; obscenity, defamation, fraud, speech that’s integral to criminal conduct. And if the speech doesn’t fall into one of those narrow categories, the government cannot restrict it, unless it can pass that incredibly tough test called strict scrutiny, which is almost always fatal.
> So how much does saying you can’t shout fire in a theater help you in doing that analysis? Not a bit. It’s empty words. Every time someone says it I get a little more misanthropic.
If you want more background, https://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_the...
So, as to whether it's illegal to shout Fire! in a crowded theater (which isn't on fire), I still don't know. The StackExchange folks lean toward it probably being illegal, especially if you end up causing a panic, depending on state. https://law.stackexchange.com/q/28853