Is low fertility a problem?

The most wrong-headed sentence I have read recently was in yesterday's Wall Street Journal:

Fertility rates have been on the decline in industrialized nations for decades, but they are now becoming a serious economic problem, felt around the globe, from the European Union to China, Japan and South Korea.

Maybe some policymakers are perceiving low fertility as a serious economic problem, but is it really a problem? I doubt it. As a serial procreator, I have never been moved by fears of overpopulation, but I am also not moved by fears of underpopulation.

If you polled top economists and asked them to name the major economic problems facing Europe, China, Japan, and South Korea, I doubt that insufficient procreation would rank high.