Earlier quoted context omitted.
Anyone absolutely can "Yell fire in a theater" in the US, this canard has an interesting history: https://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_the... You can also go on the radio and accuse your boss of whatever you like in the US as well. You might get sued by your boss in civil court, but the police will not come after you. You can also deny the Holocaust, that the earth is round, that people have lande…
The distinction between civil and criminal law isn't terribly relevant here. You can be found liable in civil court for all of the things listed in the first two paragraphs.
In the US, you can say whatever you like and you will not be prosecuted or jailed. That is simply not true in most other countries.