There was a situation (vague memory of details, here) - in which the SCOTUS decided that something is only evident of 'clear and present danger' if it directly leads to violence or harm
I think it started when a anti-semite was in a Jewish neighborhood trumpeting that the Nazis were right to exterminate the Jews.
But the court determined that all he did was give his *opinion* - he wasn't actually telling people to *kill them* so he wasn't actually inciting violence against them - since no one was hurt because of his words - he had the right to this free speech.
I'm so scratchy on the details - I'll have to look it up.
(I know that there are several cases on this issue in various natures - Nazi, etc - but I'm looking for a certain one - no luck yet in finding it)