But I am not a proponent of open borders, and I thought it would be useful to give a few fairly high level reasons why. It’s a combination of different levels of physical capital, human capital, technology, social capital, and institutions. A decent amount of immigration only changes these things slowly, but open borders could change them very quickly. It’s true the U.S. overall has undergone successful massive changes in the past, including due to large influxes of immigrants. The case against massive changes in the U.S. is also stronger today than it was in the past.

Source: Forbes February 26, 2017 16:23 UTC