In the 1926 case Whitney v. California, the U.S. Supreme Court upheld a conviction under California's Criminal Syndicalism Act which made it illegal to engage in activities promoting social or political change through violence or other unlawful means. The defendant, Charlotte Anita Whitney, was a member of the Communist Labor Party and had been convicted for aiding and abetting criminal syndicalism by organizing and assembling groups that advocated for such changes. In its decision, the court held that states could prohibit speech tending to incite crime or disturb public peace if there is clear danger that substantive evils would result from it - an application of what came to be known as "clear-and-present-danger" test. However, this ruling was later effectively overturned by Brandenburg v Ohio (1969) where stricter standards were set for laws limiting free speech rights.

In the dissenting opinion for Whitney v. California, Justice Louis Brandeis argued that freedom of speech is a fundamental right in a democratic society and should only be curtailed when there is an immediate threat to public safety or order. He contended that even if some ideas are unpopular or radical, they should still be allowed to circulate freely as part of the marketplace of ideas. This free exchange allows citizens to make informed decisions and promotes progress through competition among different viewpoints. Furthermore, he believed that suppressing speech can lead to resentment and rebellion rather than peace and stability. Therefore, unless it poses a clear danger, all speech - including advocacy for political change - must be protected under the First Amendment.