Is there language in the U.S. Constitution or other legislation that prohibits fomenting rebellion or civil war?
Not actually participating in the act of rebellion or war, just promoting and inciting it.
The Sedition Act covers some. What else is there?
Exoplanet - Since I am so ignorant, could you at least point to some of those books? I am not at all familiar with this sort of law. If you want to discuss high field magnetics, I'll be happy to. I'm sure that you'll probably be completely ignorant of some of the most basic fundamentals, just as I am completely ignorant of some areas of your expertise.
A couple of citations, please
Exo - But it appears that perhaps you have answered the question. Apparently there is no clear prohibition and it requires numerous books and Supreme Court decisions to begin to approach the subject.