I know Williamson largely through his very helpful book Conservative Bookshelf, wherein I first discovered James Burnham and realized that liberalism was indeed the ideology of Western suicide*.
Williamson remarks almost casually about something that also increasingly strikes me, the liberal hatred for human nature. Actual human nature, not an idealized form of it. Much the same attitude toward America and the West: a supposed attachment to its idealized potential combined with a loathing of its historical actuality.
Advanced liberalism demands that people think, believe, and act in ways that it is simply unnatural for human beings to think, believe, and act ...The kind of mind-training which liberalism engages in is not to be opposed to some kind of libertarian fantasy land where every man is his own man and thinks his own unencumbered thoughts. Conservative cultures likewise choose and select and perforce (!) exclude and forbid certain kinds of ideas, attitudes, etc. It's inescapeable. But I would hold that conservative cultures tend to take their cues from actual human nature rather than some fundamentally anti-human utopian faith and dogma which every day asks us to believe six impossible things before breakfast.
*Why, for example, would the Spaniards spend 800 years trying to get rid of African Muslim invaders only to invite them back in in droves? It's the liberal thing to do. And if you don't like it, you are a racist like Hitler!