My target essay at this month’s Cato Unbound is up.  From the intro:

People have been fretting about the “population problem” for at
least fifty years. But over those five decades, the perceived problem
has practically reversed. From the sixties to the eighties, the
problems on people’s minds were overpopulation and the
“population explosion.”…

During this period, libertarians were predictably quick to oppose
government action and defend individuals’ right to have as many
children as they wished.[2] But they also developed a more
intellectually creative response. Under the seminal influence of Julian
Simon, libertarians embraced the view that high and growing population
is good. The title of Simon’s most famous book became a leading libertarian slogan: People are the ultimate resource.[3]

Over the last two decades, the perceived population problem has
radically changed. Fertility has sharply fallen all over the world. It
fell in less-developed nations, deflating long-standing Malthusian
fears. But it fell in developed nations as well. Except for the United
States and Israel, every modern economy now has fertility below the
replacement rate…

Libertarians could celebrate these changes as proof that the problem
of overpopulation solves itself whether or not governments do anything
about it. But if Julian Simon and the intellectual tradition he
inspired were right, libertarians should be experiencing severe
cognitive dissonance. People with zero appreciation of Simon now worry
about low birth rates and falling populations. How can those of us who
long maintained that “people are the ultimate resource” fail to see
anything amiss?

How indeed?

P.S. Coming up: Replies by Greg Clark, Matthew Connelly, and Betsey Stevenson.