It took the Western world many generations of religious wars and persecutions before liberal thinkers, in the 17th and 18th centuries, began to challenge this imperious logic. The key to the invention of free speech was the recognition of pluralism — the fact that, in any human population, there will be people with irreconcilably different understandings of the truth. Pluralism is not relativism: I do not have to agree that there is no truth about climate change or racism or God. But I must recognize that we do not all agree on what that truth is.

The question is what to do with that disagreement. Liberalism is founded on the belief that we should tolerate one another’s error, not because we approve of it, but to avoid the violence that would result if we each sought to silence the other. The liberal believes that life is more important than truth — that it is better to live in a peaceful society full of error than in a pure society full of persecution. The price of this toleration is that we must constantly put up with hearing speech that we consider wrong; we must smother our moral instincts. As the poet Robert Lowell put it, the liberal is someone who “bites his own lip to warm his icy tooth.”

Recent events in the United States have only reaffirmed the wisdom of this liberal compromise. If there was ever a group whose speech appears to me to be obviously evil and dangerous, it is the white supremacists who marched in Charlottesville earlier this month. But the president of the United States is sympathetic to white supremacists; to him, it is the (mythical) “alt-left” that presents the real threat. If he had the power to suppress freedom of speech, he would use it to silence the people I agree with. It is better for me for no one to possess that power than to entrust it to someone who might regard me as an enemy.

Campus leftists who believe they are serving the cause of goodness and truth by silencing right-wing (or even not-so-right-wing) speakers are living in a fool’s paradise, because they temporarily inhabit an environment where they are in the majority. When they graduate into Trump’s America, they will find that many people, including people in power, think they are the ones who are wrong and dangerous. Then the principle of free speech will become their shield, as it has long shielded dissidents and radicals in America. Without it, politics becomes a war of all against all, and as we have learned since last November, there is no guarantee that the right side will win.

Adam Kirsch is a poet and a critic. His most recent book is “The Global Novel: Writing the World in the 21st Century.”