Ed Glaeser says that having kids has positive externalities:
[T]here is another reason to subsidize larger families. When parents decide to have kids, they are creating a massive benefit for their children. As much as parents may love their children, they are unlikely to reap all the benefits those children will offer during their lives. Economists often think that it makes sense to subsidize behavior that generates big “external” benefits for others: parenting seems like a particularly natural example of such behavior.
(Unless I’m misunderstanding Ed again!)
Ed is implicitly comparing the utility of having been born with the utility of never having been born. But since we do not observe those people who were never born, how can we possibly know their utility? Any theory that relies on things that are intrinsically unobservable (such as the utility of potential people who were never even conceived) seems suspect as a basis for public policy.
Actually, this may well be the easiest utility inference in the world. We know that people almost universally prefer existing to not existing because there are so many cheap and easy ways to stop existing.
As intro econ teachers might say, life is a good with free (or nearly free) disposal. Or as the great Epicurus wrote with timeless eloquence:
Yet much worse still is the man who says it is good not to be born, but
“once born make haste to pass the gates of Death.” [Theognis, 427]
For if he says this from conviction why does he not pass away out of life? For it is open to him to do so, if he had firmly made up his mind to this. But if he speaks in jest, his words are idle among men who cannot receive them.