It's a reasonably convincing argument. It won't change the equilibrium size of our household as we don't think we can afford the additional childcare expenditures and we'd likely need a bigger house. And if your consumption bundle requires family trans-Pacific travel, additional kids are definitely not low marginal cost.
But I've been most surprised at one of the more common lines of critique he's been getting in comments. Here's a representative selection.
Boy, what an appropriately named book. I'm amazed that with dwindling natural resources your show would promote the selfish (and environmentally irresponsible) act of having more than two children in a family. That makes me one of a very significant minority, but I don't think it's something to brag about in the current environment. At some point, societies are going to have to address the spread of humans is having on the planet--not unlike a virus.128 people "recommended" this comment over at the New York Times:
There are great reasons to have fewer children, or none. Overpopulation, for one--and it's behind so many of the other social problems we have. ...I didn't see any such comments over at the Wall Street Journal.
Even if you want to come down on the side of the folks freaking out about population, middle to upper class Americans having more kids is hardly the cause of any problems. It's far more likely rather to be a solution.
Caplan's talking to Trevor and Carol, the couple who hesitated too long and had no kids, not to Clevon, whose great great great grandkids wind up starring in "Ow My Balls!" It's mildly insane to think that his argument, directed as it is, does harm by contributing to overpopulation.
The more kids Bryan and Corina have, the better for everyone else.
Will Wilkinson's critique misses the mark as well, and more widely if you consider just how damned good he is on everything else.
Economists generally begin from the assumption that we’re rational decision-makers who do the best we can to achieve our aims given the constraints we face. In Mr. Caplan’s previous book, “The Myth of the Rational Voter,” he lays out an elaborate theory of “rational irrationality” in order to explain how it is possible for voters to act on irrational beliefs about politics and policy without having to abandon the economist’s foundational rationality assumption. But Mr. Caplan offers us no analogous theory of the rationally irrational mother. He simply begins with the ad hoc hypothesis that mothers are forgoing body-reconfiguring pregnancy, excruciating childbirth and the massive time-cost of additional children (which women disproportionately shoulder) not because they are rational beings taking into full account the manifold considerations relevant to profoundly life-shaping choices, but because they are in error about the power of parenting to shape “adult outcomes.” I like it better when Mr. Caplan reasons like an economist.All that is required for Caplan's argument to hold is that parents largely misattribute good outcomes to high parental effort when high parental effort generally is confounded by good genes. The misattribution leads to overestimation of the amount of effort required for good outcomes and consequently leads parents to perceive the marginal effort cost of acceptable quality children as being higher than it really is. If the amount of effort needed for good outcomes is really lower than folks think, at least some of those people will be having fewer than their optimal number of children. Caplan's not trying to convince folks like Will to have children - best evidence suggests he sees them as a bad rather than a good; rather, he's trying to convince the folks who already like kids and are waivering about having one (another) because of the costs.