At City Journal:
And in a certain sense, the promise of the Enlightenment has been triumphantly fulfilled in our modern societies—surely as regards natural evil. Thanks to rational inquiry, to take but one instance, the infant-mortality rate since Jenyns wrote has fallen 98 percent. We live lives cleaner, more comfortable, and freer from pain than those of any people who have ever existed. Nobody today has to endure one-hundredth of the physical tortures, brought by illness and the efforts to treat it, that Philip II of Spain and Charles II of England had to endure.
Nor can one say that no moral advance occurred because of the Enlightenment. Just as we are freer from disease, so, too, our mental lives are freer. Of course, dictatorships over thought still exist in the world, but they are on the defensive and have come to seem somehow unnatural. Freedom is now the default setting of human thought. No one can tell us what to think, say, or write, at least not without our consent.
But an uninvited guest has arrived at this banquet of human advancement: evil. Whether men behave better or worse, individually or in the aggregate, than they did before the Enlightenment, is probably a question that we cannot answer approximately, let alone definitively. But what is certain is that moral evil has not only failed to disappear but has taken on a more deliberate, calculated character. Whereas the torturers of Damiens did their evil unself-consciously because it was the natural or preordained thing to do, modern evil is done after intellectual reflection, divorced from any tradition that might guide conduct.
The two greatest moral catastrophes of the twentieth century, wrought by Lenin and Hitler, were perverse effects of the Enlightenment. Lenin and Hitler were creatures of the Enlightenment not in the sense that they were enlightened, of course, but in the sense that they believed they had the right and the duty to act in accordance with their own unaided deductions from their own first principles. Everything else they regarded as sentimentality. Lenin preached no mercy to the non-proletarian, Hitler none to the Jew. The truth of their theories, supposedly rational and indubitable, was more evident to them, more real in their minds, than the millions killed as a consequence of those theories. If a syllogism ended in a command to commit unspeakable evil, you did not doubt the premises or the argument but obeyed the command.