The ultimate good desired is better reached by free trade in ideas—that the best test of truth is the power of the thought to get itself accepted in the competition of the market. . . . That, at any rate, is the theory of our Constitution. It is an experiment, as all life is an experiment. . . . While that experiment is part of our system, I think we should be eternally vigilant against attempts to check the expression of opinions that we loathe . . . unless . . . an immediate check is required to save the country.74
