Family Externality

Ed Glaeser:

I am also unenthusiastic about eliminating tax preferences for larger families. Most people seem to think that giving tax relief to bigger families is a matter of simple fairness. As an economist, I lack standing to make proclamations about fairness, but there 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.

Externality abuse.