[W]hen men have realized that time has upset many fighting faiths, they may come to believe . . . that the best test of truth is the power of the thought to get itself accepted in the competition of the market, and that truth is the only ground upon which their wishes can safely be carried out. That, at any rate, is the theory of Constitution. It is an experiment, as all life is an experiment.
Mr. Justice Oliver Wendel Holmes; Abrams v. United States