In tight markets, poor and middle-class households are forced to compete with each other for scarce homes. And so new market-rate housing eases that competition, even if the poor aren’t the ones living in it. Over time, new housing also filters down to the more affordable supply, because housing becomes less desirable as it ages. That means the luxury housing we’re building today will contribute to the middle-class supply 30 years from now; it means today’s middle-class housing was luxury housing 30 years ago.