Suppressing Speech Harms
John Stuart Mill thought that suppressed speech harms in multiple ways:
But the peculiar evil of silencing the expression of an opinion is, that it is robbing the human race; posterity as well as the existing generation; those who dissent from the opinion, still more than those who hold it. If the opinion is right, they are deprived of the opportunity of exchanging error for truth: if wrong, they lose, what is almost as great a benefit, the clearer perception and livelier impression of truth, produced by its collision with error.
John Stuart Mill, On Liberty, rev. ed. (Boston: Ticknor and Fields, 1863) 35–36