One implication is that helicopter parents can relax a little: they’re probably not having as big of an effect on their children’s personality as they think, and they’re almost certainly confusing causation and correlation in assessing how well or poorly they’ve done as parents as they watch their children age.
Another implication Caplan draws is that there are, as his book title suggests, Selfish Reasons to Have More Kids. This may be true, but what I argue in an essay at Quillette is that there may also be altruistic reasons to have more kids, especially if we are worried about environmental issues like climate change. Contrary to a thought common among journalists, the environmental pollution that new children create is not a good reason for conscientious parents to have fewer kids.
Economists since Julian Simon have defended the benefits of population growth, though the case for natalism is more nuanced than Simon thought. A lot depends on who is having the children, and under what kinds of political institutions they live.
As readers of BHL know, the world does not contain a fixed supply of resources, so that creating more children automatically leaves fewer resources and more pollution for other people. Instead, children born to successful and compassionate parents who live under political institutions that foster trade are the ultimate resource for transforming the existing stock of resources into more and better resources, including medicine, books, and technology that reduces pollution rather than just creates it.
In other words, if you care about the welfare of future people, and are reading this blog post, the world would probably be better off if you had more kids.