Excerpt: If only out of pure self-interest, we shouldn’t just be willing to hear the arguments of those with whom we disagree, we should be eager to. Without letting them speak, you can’t know where they stand, and, to paraphrase John Stuart Mill’s famous quote from On Liberty: If you don't know the other side's argument, you really don't know much of your own, either.
Of course, the problem is that many people think they already know everything they need to know. In fact, they’re certain of it. When you have moral certainty, you can presume the authority to shut people down.