There have been instances in U.S. history where the government has attempted to ban speech that people used to advocate for societal change. In some past cases, the U.S. Supreme Court upheld punishment of expression that advocated for change, especially if the speaker called for a revolution or other forms of illegality.
Much broader protection exists for the freedom of expression today. There are exceptions for speech that incites people to violence, but they are very narrow. In Brandenburg v. Ohio (1969), the U.S. Supreme Court held that “the constitutional guarantees of free speech and free press do 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.” Subsequent Supreme Court cases have clarified that speech advocating illegal action at some indefinite future time is protected by the First Amendment, if it does not constitute criminal conspiracy. These rulings ensure that people can advocate for different forms of societal change, free from government reprisals.