“Real freedom is freedom from the opinions of others. Above all, freedom from your opinions about yourself.”

Source: Sceptical Essays

Source: Posted on @angelovulpini, Instagram (June 3, 2019)

Variations of this quote are often attributed to Stevenson without a date or location for the remark. Two early occurrences are in a Congressional hearing on November 13, 1985, where Stevenson was quoted by Representative Ted Weiss ("Limits on the Dissemination of Information by the Department of Education" (1986), published by the GPO); and an article dated June 4, 1989 by Sue Ann Wood in the St. Louis Post-Dispatch ("Write Editor, Readers Urged"). No source closer to Stevenson has been found.
Disputed

Nobel Peace Prize Speech (1975)

Collected Works, Vol. 30, pp. 107–117.
Collected Works

Address at the National Archives dedicating a shrine for the Declaration of Independence, the Constitution, and the Bill of Rights (15 December 1952) https://trumanlibrary.org/calendar/viewpapers.php?pid=2102
Context: Of course, there are dangers in religious freedom and freedom of opinion. But to deny these rights is worse than dangerous, it is absolutely fatal to liberty. The external threat to liberty should not drive us into suppressing liberty at home. Those who want the Government to regulate matters of the mind and spirit are like men who are so afraid of being murdered that they commit suicide to avoid assassination.
All freedom-loving nations, not the United States alone, are facing a stern challenge from the Communist tyranny. In the circumstances, alarm is justified. The man who isn't alarmed simply doesn't understand the situation — or he is crazy. But alarm is one thing, and hysteria is another. Hysteria impels people to destroy the very thing they are struggling to preserve.
Invasion and conquest by Communist armies would be a horror beyond our capacity to imagine. But invasion and conquest by Communist ideas of right and wrong would be just as bad.
For us to embrace the methods and morals of communism in order to defeat Communist aggression would be a moral disaster worse than any physical catastrophe. If that should come to pass, then the Constitution and the Declaration would be utterly dead and what we are doing today would be the gloomiest burial in the history of the world.

1963, Third State of the Union Address