Elon Musk is looking at fertility rates and capitalism. Most of the developed world has fertility rates around 1.5. ( 2.4 or 2.5 is considered the replacement rate.) The fertility rate in the 1960s used to be around 4.5 https://worldpopulationreview.com/country-rankings/total-fertility-rate

What this means is there will be a whole bunch of unproductive old people, and fewer and fewer productive young people. Capitalism is going to collapse because we cannot maintain ever increasing amounts of production and consumption. Debt is putting off payment into the future. If future money is declining debt will collapse and with it Western economies.

Capitalism is like a fungus, it grows or it dies.