It’s not an EXCEPTION but it is an actionable offense.
If people are injured or killed based on YOUR perfectly legal free speech, you are liable.
Just like you are liable for libel, slander, perjury, and other things that you have an absolute freedom to say.
“It’s not an EXCEPTION but it is an actionable offense.”
It could be. Not always. If there’s an actual fire, for example, then there’s nothing actionable. In fact, just the opposite, you might be liable if you knew there was a fire and didn’t warn anyone.
except that perjury is a crime, libel/slander are explicitly civil offenses-
yelling fire in a movie theater is neither a crime nor a civil offense itself.