the legal line between saying something dangerous and actually trying to make something dangerous happen right now.
in brandenburg v. ohio in 1969, the supreme court ruled that even advocating violence or illegal activity can be protected speech unless it is intended to provoke imminent illegal action and is actually likely to do so.
the interesting part is that this protection came from a case involving a ku klux klan leader.
sometimes the strongest free speech rules come from protecting speech almost nobody wants to defend.