The aim in an open society is not to put up with ideas with which we disagree. It is to take them seriously and to criticize them—not necessarily as a way of condemning them, but as a way of trying to understand them, and of testing whether or not they are true, and learning from them, even if learning from them means learning how and where they go wrong.
This is what Popper meant when he said that open society is ‘based on the idea of not merely tolerating dissenting opinions but respecting them.’ Open society is based on respect for other people, for their freedom and autonomy as rational agents—or, as Kant would have put it, for people as ends in themselves. It is not that we regard their ideas as evils that we have to tolerate for civility’s sake. And it is not even that we regard them as the ideas of other people who have just as much right to ideas as ourselves. That, at best, would be paternalism. And it would have nothing at all to do with a recognition of our own fallibility. Respect, on the contrary, means that we take the dissenting opinions of others seriously, and that we regard them as possibly true. It means, in fact, that we treat them as potentially our own—since we want to discover the truth and since we recognize that we may be in error—and it means, for this reason, that we try to do everything in our power to criticize them and to show that they are false.