“Oscar: In a society where dissenting viewpoints are suppressed, those viewpoints are potent and dangerous… Where dissent is tolerated, it rapidly becomes quaint and is viewed as un-sophisticated; people merely amuse themselves with the expression of contrary opinion.”

Concurring, Graves v. New York ex rel. O'Keefe, 306 U.S. 446 (1939).
Judicial opinions

Oliver Wendell Holmes lecture delivered at Harvard (1958); quoted in The Rhetoric of Our Times (1969) by J. Jeffery Auer, p. 124.
Extra-judicial writings

Slaves of Time (p. 19)
Short fiction, The Robot Who Looked Like Me (1978)

Interview with the New York Times (29 October 1973)
Other speeches and writings

Pages 40-1.
The Case for Democracy (2004, with Ron Dermer)

Alan Rusbridger (2008) on The Guardian priorities, cited in: Richard Lance Keeble, John Tulloch, Florian Zollmann (2010) Peace journalism, war and conflict resolution. p. 301.
2000s

My Day (1935–1962)
Context: What is going on in the Un-American Activities Committee worries me primarily because little people have become frightened and we find ourselves living in the atmosphere of a police state, where people close doors before they state what they think or look over their shoulders apprehensively before they express an opinion.
I have been one of those who have carried the fight for complete freedom of information in the United Nations. And while accepting the fact that some of our press, our radio commentators, our prominent citizens and our movies may at times be blamed legitimately for things they have said and done, still I feel that the fundamental right of freedom of thought and expression is essential. If you curtail what the other fellow says and does, you curtail what you yourself may say and do.
In our country we must trust the people to hear and see both the good and the bad and to choose the good. The Un-American Activities Committee seems to me to be better for a police state than for the USA. (29 October 1947)