The old atheists, like Nietzsche, knew what happened when a civilization abandons its spiritual foundation:
"A people that still believes in itself retains its own god. In him it reveres the conditions which let it prevail, its virtues: it projects its pleasure in itself, its feeling of power, into a being to whom one may offer thanks. Whoever is rich wants to give of his riches; a proud people needs a god: it wants to sacrifice. Under such conditions, religion is a form of thankfulness. Being thankful for himself, man needs a god." (The Antichrist, section 16, Kaufmann translation)As Eric Voegelin said, the classical liberals were people who thought they could destroy a civilization just a bit, and then halt the process of destruction whenever they wanted it to halt. But Nietzsche saw much more clearly than they did: "The moral and social order to which the religion gave rise cannot survive its disappearance."
Consequently, a culture that doubts its religion comes to doubt itself and its own legitimacy. And a culture that repudiates that religion is, in effect, committing a kind of cultural suicide. The moral and social order to which the religion gave rise cannot survive its disappearance. The trouble, in Nietzsche’s view, is that too few see what this entails:
"Much less may one suppose that many people know as yet what this event [the death of God] really means -- and how much must collapse now that this faith has been undermined because it was built upon this faith, propped up by it, grown into it; for example, the whole of our European morality." (The Gay Science, p. 279)
As we continue our descent into societal chaos, today's progressive liberals will surely be shocked by and completely unprepared to deal with the convulsions that ensue, and will never, ever connect it to their own continued efforts to hack away at our civilization's foundations.