In a blog post titled Net Externalities: Immigrants versus Children, Adam Ozimek compares the externalities of immigrants with those of children. An excerpt:

This begs the question of the externalities of immigrants. After all, positive externalities for natives probably don’t start appearing until after high school or college, and before that they are on average consuming far more than they produce.

Since the average immigrant age is around 30, that means when they’ve arrived they are already past the stage when they just consume society’s resources, and have begun producing externalities. Doesn’t this suggest that positive externality of immigrants is even larger than that for natives? If you’re going to claim that the average lower education level of immigrants reduces their externalities, keep in mind that immigrants are also more likely to be small business owners and PhDs than natives.

It’s interesting that when immigration is discussed economists quickly jump to the debate about the impact on native wages. I doubt that the 72% of economists above believe that the average externality of people is smaller than 6% of the wages of highschool dropouts, which is around the lowest credible estimate in the literature, so why don’t economists accept that externalities of immigrants trump wage effects and quickly move to arguing for more immigration?

Bryan Caplan approvingly quotes Ozimek in a blog post titled Of Infants and Immigrants, and adds:

Another objection is that immigration creates positive externalities for the country of destination, but negative externalities for the country of origin. But when you remember remittances, the objection falls flat. Workers do a lot more for the Third World by leaving than staying.