We struggle to explain large scale long term cultural changes. Such as the rise and fall of empires, or the demographic transition. Yes, we do seem to find patterns that are somewhat predictable, but our abilities here are also clearly limited.
We should thus take seriously a simple model of culture: random drift. What if:
(A) Poor rural small scale societies tend to be locally stable and to face strong/fast selection pressures due to competition with local rivals. They are thus consistently functional for that context.
(B) Rarely, poor rural small societies drift into cultural states conducive to becoming large, rich, and/or dense.
(C) Societies that are large, rich, and/or dense face weaker/slower selection pressures, have strongly spatially-correlated internal cultures, and also consistently generate internal fashion-like dynamics that induce their shared culture to wander in the vast space of possible cultures, and
(D) Random places in the space of possible cultures are pretty dysfunctional, and cause slow societal collapse.
Together these assumptions predict the rise and fall of civilizations, and that our current civilization has probably been drifting toward dysfunctional states. Falling fertility is plausibly one cultural element that has been drifting dysfunctional, but there may be many others.
This theory supports traditional conservative complaints wary of allowing fast big cultural changes, though putting them in charge doesn’t obviously solve the fundamental problem here. Futarchy might solve this, if our culture liked it, and was willing to be suspicious of its natural cultural changes. Alas these seem unlikely.
Added 1Nov: Anders Sandberg sims a simple model of this.
"Things out of perfection sail"
I had never heard of "futarchy," which just shows that I'm fifteen years behind in my buzzwords.
https://en.wikipedia.org/wiki/Futarchy