*<p>I reiterate a former reply to this exact article.<p>I am unbribed. I suspect this is an example of Troll Science for economists.<p>1. The question becomes: if it is economical then why isn't it the case from the start. Why do nations exist? Why do they have borders?<p>What of the question posed by a famous economist: why do corporations exist? Why not a market filled with nothing but traders? The answer isn't obvious but there is an answer. Perhaps free movement has similar invisible overheads that are being conveniently ignored.<p>2. Ignoring what I've said above for a moment. Let us suppose that free movement made us richer. Then nations would be competing, offering incentives to all.<p>They do not. Only to a tiny percentage of the population with obviously valuable skills or assets. That implies that there is a very high price before externalities are sufficiently alleviated. It at least means governments think that is so for whatever reason.<p>3. Within nations we have rich and poor zipcodes. It is true that workers from poor neighbourhoods travel to richer ones for work, it is basic time/money arbitrage. Yet few people think of installing poorer workers in richer neighbourhoods as a means to improve the economy. Why is that?