… is from page 190 of my colleague Chris Coyne’s superb 2013 book, Doing Bad by Doing Good :
The logic behind allowing labor migration is straightforward. Decisions need to be made regarding the allocation of labor, which, like other goods and services, is a scarce resource. Open migration not only expands the range of potential choices available to individuals – the essence of economic freedom – but allows for the reallocation of labor to its highest-valued use across a more extensive range of alternatives. In other words, removing barriers to migration allows people to discover the highest-valued use of their labor and thereby contributes to broader economic development. Indeed, the potential contribution of migration to global economic wealth is staggering.