For most of American history, the courts held that no one has a right to advocate violations of the law. They ruled that advocacy of crime is wholly outside of the First Amendment--akin to a criminal attempt and punishable as such. Indeed, many of the judges revered as the strongest champions of free speech believed that express advocacy of crime was punishable. Judge Learned Hand, in his great 1917 opinion in Masses v. United States, established himself as a true hero of free speech by saying that even dangerous dissident speech was generally protected against government regulation. But Hand himself conceded that government could regulate any speaker who would "counsel or advise a man" to commit an unlawful act.
...in the Court's 1969 decision in Brandenburg v. Ohio. There the Court said the government could not take action against a member of the Ku Klux Klan, who said, among other things, "We're not a revengent organization, but if our President, our Congress, our Supreme Court, continues to suppress the white, Caucasian race, it's possible that there might have to be some revengence taken." The speaker did not explicitly advocate illegal acts or illegal violence. But in its decision, the Court announced a broad principle, ruling that the right to free speech does "not permit a State to forbid or proscribe advocacy of the use of force or of law violation except where such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action."
http://prospect.org/article/violent-speech-right