Matthew Yglesias has a post up on the stimulative effects to the economy of legalizing various activities. Item 7 is “Liberalized immigration”.

Undoubtedly, this will grow the GDP. That is not the question. The question is whether it will grow the per capita GDP, which is how the overall benefit to society should be defined.

As I noted before, the post Black Death prosperity in Europe was almost certainly at a lower aggregate GDP than before the plague, but because population fell faster than GDP, wages, and standard of living, went up.