From the Canadian Century Initiative to Bill Clinton, “we need immigration to compensate for the low birth rate” is a common refrain. Those pushing this line rarely list the problems of population decline1 that immigration supposedly solves. Instead, we’re seduced by the notion that the economy or society is a sort of angry god that must be placated by additional human fuel, whatever the source. The population number going down is bad; immigration brings the population number up; therefore we need more immigration. (Composition isn’t mentioned.) Implicitly, this is a blank-slatist argument, relying on the fact that honest discussion about ethnic differences is excluded from public discourse.
Making a state’s population go up for the sake of it is meaningless paper-clip maximizing. Once you start looking at the reasons why a growing population might be beneficial (to an individual member of society or the proverbial social planner), it becomes clear that actually-existing immigration2 makes the problems of population decline worse, not better.
Effect on population ageing
The first thing to understand is that most of the problems of population decline, like pensions bankrupting the state or less innovation and entrepreneurship, are actually problems of population aging. That’s what separates the present decline, which is the result of low fertility, from past episodes such as the Black Death, which were caused by high mortality. Both involve decline, but in the latter case the survivors were youthful and vigorous and could bounce back quickly.
The thing is: immigrants age too. This means that while immigration can definitely reverse population decline, it can’t do much for population aging. Assuming immigrant age-structure and fertility remain constant, the difference in the working-age share of the population in 2060 between zero net migration and 2019 levels of migration in the United States is… 2% (57% vs 59%).3
