Jason Stanley in the Boston Review:
What are the limits of freedom of speech? It is a pressing question at a moment when conspiracy theories help to fuel fascist politics around the world. Shouldn’t liberal democracy promote a full airing of all possibilities, even false and bizarre ones, because the truth will eventually prevail?
Perhaps philosophy’s most famous defense of the freedom of speech was articulated by John Stuart Mill, who defended the ideal in his 1859 work, On Liberty. In chapter 2, “Of the Liberty of Thought and Discussion,” Mill argues that silencing any opinion is wrong, even if the opinion is false, because knowledge arises only from the “collision [of truth] with error.” In other words, true belief becomes knowledge only by emerging victorious from the din of argument and discussion, which must occur either with actual opponents or through internal dialogue. Without this process, even true belief remains mere “prejudice.” We must allow all speech, even defense of false claims and conspiracy theories, because it is only then that we have a chance of achieving knowledge.
Rightly or wrongly, many associate Mill’s On Liberty with the motif of a “marketplace of ideas,” a realm that, if left to operate on its own, will drive out prejudice and falsehood and produce knowledge. But this notion, like that of a free market generally, is predicated on a utopian conception of consumers.
More here.