““Since it is impossible for us to know, prior to engaging in a discussion, which opinion is true and which is false, it is dangerous to entrust the government with the power to suppress what it believes to be falsehood; for that purported falsehood may turn out to be the truth. In any event, truth can be ascertained only by the full airing of views on all sides; in the absence of such an airing, even a true belief can become stale and lifeless.””
