There’s a theory about housing that has taken hold with a kind of religious fervor: If you want to make housing more affordable, just build more of it. Supply and demand. Simple economics.This narrative is now dominating housing policy discussion across the political spectrum. Deregulate, upzone, speed up approvals, let the market work. And if you build enough homes, the theory goes, prices will come down.But here’s the question almost no one asks: What happens when prices actually start to fall...