One of the reasons people voted for Brexit was to “take control of our borders”. Around the world, western leaders are echoing a similar message. It seems migrants are viewed more as a drain on resources than a boost to the economic output of a country. At the other end of the spectrum, there are some who argue that the world should have complete labour mobility and, if people could live where they wanted, then world GDP would double. Phil Dobbie asks Prof Steve Keen where this the optimum point on the spectrum. Is labour mobility a good thing or a bad thing?