In the face of shrinking populations, many of the world's major economies are trying to engineer higher birth rates.

Policymakers from South Korea, Japan and Italy, for example, have all adopted so-called "pronatalist" measures in the belief that doing so will defuse a demographic time bomb. These range from tax breaks and housing benefits for couples who have children to subsidies for fertility treatments.

But here's the thing: Low—or, for that matter high—birth rates are not a problem in and of themselves. Rather, they are perceived as a cause of or contributor to other problems: With low birth rates come slow economic growth and a top-heavy age structure; high birth rates mean resource depletion and environmental degradation.

Moreover, birth rates are notoriously hard to change, and efforts to do so often become coercive, even if they don't start out that way.

As demographers and population experts, we also know that such efforts are usually unnecessary. Manipulating fertility is an inefficient means of solving social, economic and environmental problems that are almost always better addressed more directly through regulation and redistribution.

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