This is not legal advice but I think they are. See Brandenburg v Ohio.
"Brandenburg was convicted of violating a criminal law that prohibited speech that advocates crime, sabotage, violence, and other similar acts after he spoke at a KKK rally. The Supreme Court found that the law infringed on Brandenburg's First Amendment rights, and created the imminent lawless action test. In order for speech to fall out of First Amendment protection, it must 1) be directed at producing imminent lawless action and 2) it is likely to produce such action."
I think there is an exception for ones made against certain public officials, which IMO are likely unconstitutional, but no one is really excited about challenging those.