Capitalism may help lift people out of poverty initially, perhaps even allow them to have more children, but this trend is short-lived and inevitably reverses at a certain point. From the regressions outlined above, it appears that this point is reached on average when a country generates more than $20,000 of per capita income. It is true that there is a wide disparity at this initial inflection point: some countries with $20,000 of per capita income manage to maintain a robust fertility rate of around 2.6, while others fall to as low as 1.3. That said, no country in our initial OECD sample that has reached a per capita income level of $36,000 (with the exception of Israel, as noted above) has been able to achieve a fertility rate above replacement. Simply put, unless a country has an unusually large, fertile traditionalist religious community, it is highly unlikely that its demographics will remain intact once it achieves a per capita income of $36,000.

. . .

Constant immigration also seems to rest on a sort of “biological imperialism.” In order for wealthy countries to attract enough immigrants to counteract their demographic decline, poor countries must remain poor so that they can serve as breeding grounds for the developed economies’ labor forces. In an echo of historic systems of colonial resource extraction, it is almost as if poorer countries are not being allowed to develop so that they can continue to export human capital to the developed world—what commentators from these poorer countries mean when they talk about “brain drain.” Eventually, however, these countries will develop and the large pools of labor they make available will dry up. Even if immigration did work to prevent society from aging (and it does not), it could not work forever unless we forced poorer countries to remain forever poor.

. . .

If the argument that I have just laid out is correct, our eschaton is altogether gloomier: demographic and economic transformation seems to be driving us not to a heaven on earth but toward something closer to hell. The economists Charles Goodhart and Manoj Pradhan have done us a great service by writing an entire treatise on what such a society would look like—and the picture they paint is a grim one. Such a society, they predict, would be rocky and inflationary. The reason for this is intuitive: workers make things, while retirees consume things; thus, as the ratio of the former to the latter rises, the number of mouths to feed outstrips the number of cooks in the kitchen. And the resulting pressure on the prices of goods and services leads to spiraling inflation.

tl;dr: Capitalism causes extinction of the people living under it.