History should teach us then, that in times of high emotional excitement minority parties and groups which advocate extremely unpopular social or governmental innovations will always be typed as criminal gangs and attempts will always be made to drive them out. It was knowledge of this fact, and of its great dangers, that caused the Founders of our land to enact the First Amendment as a guarantee that neither Congress nor the people would do anything to hinder or destroy the capacity of individuals and groups to seek converts and votes for any cause, however radical or unpalatable their principles might seem under the accepted notions of the time.

Hugo Black (1886-1971) American politician and jurist, US Supreme Court Justice (1937-71)

Barenblatt v. United States, 360 U.S. 109, 151 (1959) [dissent]
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