This is an insightful article, although I have the same quibble as you. People had children during the centuries when life for most of us was "nasty, brutish and short." People in Europe are deciding not to have children because they are secular, materialistic, narcissists.
But the great point this article makes is the impact on the economy when population growth drops past replacement. Two thirds of the Western economy is dependent on consumer spending. Consumer spending is fueled by young and middle aged adults, who are in the acquisition phase of life and many of whom are raising families. Older and retired adults tend to live off the assets they acquired earlier and spend much less on consumer goods. This trend has hit Europe, Japan and European-Americans. Immigration (and the State of Utah), however, have kept America much younger demographically, which fuels economic growth.
I'm really surprised no one has linked the interminable Japanese recession or the stagnation in Europe to the problem of their greying populations. OK, I guess it's not so surprising since liberal CW says the problem is overpopulation and they haven't come to grips with the fact that population growth has been slowing since WWII and according even to the UN will peak worldwide in 2050. Liberals are always playing catch up with the facts.
But the great point this article makes is the impact on the economy when population growth drops past replacement. Two thirds of the Western economy is dependent on consumer spending. [Sure, ultimately, all of it depends on cumsumer spending --- TQ] Consumer spending is fueled by young and middle aged adults, who are in the acquisition phase of life and many of whom are raising families.
I am afraid this is a speculation, however. Firstly, the ecomomy can move along just fine by replacing the old stock with new; one does not need expansion of the population for the growth of economy.
Secondly, it is a misconception that the young people "fuel the economy." It may be based on the misleading observation that businesses target the young, but this is often because the latter are influencers, not necessarily buyers. To the contrary, it is people over 40 that are in their prime of the earning power and the retirees who spend out of wealth --- these are the people who pay.
Finally, what you posit is the economy of scale: that efficiency is higher in a larger population than in the smaller. I do not think anyone has observed such economies or diseconomies.
I'm really surprised no one has linked the interminable Japanese recession or the stagnation in Europe to the problem of their greying populations. This is because another, more plausible reason is readily available: in both cases the population is unwiling to abandon broken, outdated institutions. In teh case of Japan, for instance, plenty of advisors told them what to do, but the instructions are simply not culturally acceptable. In Germany, similarly, most economists, including those who advise the government, knew for quite some time that the the traditional, paternalistic state is no longer viable. This too is not culturally acceptable yet.
The difficulty is a fundamental one: suppose you have perfect foresight and knowledge, how do you lead an ignorant populous?
When it comes to masses, knowledge is not as important as sentiment. Consider, for instance, that our Constitution is in plain view for two centuries, hence known, yet no country bothered to adopt its basic elements. This is becuase the sentiment in those countries lies elsewhere; ignorance is clearly not the ussue.