Commentary The great voice of intellectual diversity is John Stuart Mill, who in “On Liberty” (1859) warned that uniformity of opinion in a society damaged free speech and free thought. Mill was a renowned liberal of the Victorian Age who argued for progressive causes throughout his career, but he understood well the complacency and blindness that set in when people go through their lives never facing challenges to their outlooks, and that included challenges from the right. Suppression of unpopular opinion without giving it a chance to be fairly heard harms everyone, he insisted. Yes, those unfortunate people adhering to a belief that the society will not admit into the public square suffer a direct injury (their pamphlets seized, employment denied, prosecution …), but the suppression injures everyone else as well. Here’s how Mill put it: “But the peculiar evil of silencing the expression of an opinion is, that it …