The limitations Cletus, are described through history of the SCOTUS decisions— which is what was mentioned. Not in the Constitution, which protected all speech, tar and feathers and the very basis of our Revolution from the British Empire of George IIIrd. Understood, and thanks for the clarification.
Such is the weakness of Marbury v Madison being used as the “gold standard” of Constitutional law.
As I learned in my Law classes.
The Court then is allowed to (re)define the very document that created it.
To wit, if the SCOTUS had opined that shouting “fire” in a crowded theater WERE “illegal” speech, Congress should have moved forthwith to codify it in Law.
Since they did not, it cannot be considered “illegal”.
In the current atmosphere, such things turn out to be protected by unConstitutional rules and regulations (not “laws”, per se) that throw legal fences around such things as use of the word “ni88er”.