Ingrid Norton:

Pinker recognizes World Wars I and II as big problems for his thesis that modernity lessens violence. Though far from the only mass atrocities in human history, these conflicts entail some of the most densely violent years in the annals of bloodshed. Pinker asserts that despite this, the détente that occurred afterwards was more durable: The “enduring moral trend of the [20th] century was a violence-averse humanism that originated in the Enlightenment, became overshadowed by counter-Enlightenment ideologies wedded to agents of growing destructive power, and regained momentum in the wake of World War II.”

Confirmation bias much? Yeah, I have to agree with what others have said about this book: it’s more than a little specious to pretend that “the Enlightenment” only encompasses those strains of thought that happen to appeal to us today. As Isaiah Berlin stressed repeatedly, a large number of Enlightenment thinkers accepted that Newton’s accomplishments in physics could be duplicated in ethics, that “true” answers to normative questions could be obtained through rational inquiry, and that if one persisted in clinging to worldviews which had been discredited scientifically, they were not simply mistaken but possibly perverse, and perhaps a liberal application of force was needed to make them see the error of their ways, or at least clear their outdated detritus off of the shining path of progress.
Some thinkers who epitomized the sort of Enlightenment ideals that Pinker values, like Voltaire and Fontenelle, hewed to an “original sin” conception of humanity as hopelessly corrupt and weak, needing strong, enlightened guidance from elites. Jacobins, Bolsheviks and Maoists followed suit. Even Nazism wasn’t quite the “counter-Enlightenment” movement that Pinker seems to imply. Opposed to ideas of toleration and personal freedom, yes; but they shared a belief with many progressives of the age in eugenics in particular, or more broadly, in the application of science to purify humanity in order to achieve its glorious future destiny. There really isn’t a neat dividing line between the Enlightenment, the Romantics, progressives, and reactionaries, and no reason to think that one will ever appear.