Another blow to pro-immigration arguments.
Read here. Abstract, emphasis added:
Longer lives and fertility far below the replacement level of 2.1 births per woman are leading to rapid population aging in many countries. Many observers are concerned that aging will adversely affect public finances and standards of living. Analysis of newly available National Transfer Accounts data for 40 countries shows that fertility well above replacement would typically be most beneficial for government budgets. However, fertility near replacement would be most beneficial for standards of living when the analysis includes the effects of age structure on families as well as governments. And fertility below replacement would maximize per capita consumption when the cost of providing capital for a growing labor force is taken into account. Although low fertility will indeed challenge government programs and very low fertility undermines living standards, we find that moderately low fertility and population decline favor the broader material standard of living.
This is a complex subject, and, of course, the major argument against alien immigration is that of ethnic genetic interests (ultimate interests), followed closely by the primary proximate interest of culture/civilization, and then followed by various other significant proximate concerns regarding sociopolitical power, and then, finally, economics.
The point here is that even the economic arguments fail the pro-immigration argument: higher standards of living can be achieved with a declining population, as long as the rate of decline is not too extreme and the fertility rate is not too low. There is certainly no reason for hysterical panic, re: low fertility, as long as the gates can remain closed to replacement immigration. Tweaking social policy to raise fertility rates to close to, or at, replacement levels can be sufficient to ensure robust standards of living for Western populations. Ponzi schemes of bloated gross "economic growth" due to increased population size should be eschewed.