Also, there is little or no discussion of the objective fact that the recent rapid rise in global population has been accompanied by an even faster increase in GDP per capita—the pie is growing larger despite its being cut into more slices. Of course (all together now!) correlation isn’t causation, but it may be equally the case that a shrinking population will be accompanied by an even faster decline in wealth, resulting in a collapsing standard of living unrelated even to the costs of supporting an aging population. This may be particularly the case when our technological infrastructure is supported by vast division of labour into a multitude of specialities which, as population shrinks, there may not be enough people to fill and/or train successors.
See also the 2023-08-28 post, “What Does a Declining Population Mean for Economic Growth?” for an argument why declining population can reach a steady state in which technological innovation comes to a complete halt and economic growth shifts into decline, leading to an Empty Planet scenario.