The mortgage-interest deduction is the backbone of American housing policy. It exists, ostensibly, to encourage widespread homeownership. In its favor, it doesn’t actually do that. But it does have consequences: It’s been one of the quieter causes of the housing bubble. The mortgage-interest deduction deserves special recognition for the stupidity with which it subsidizes something that should not be subsidized in the first place. I challenge you to design a subsidy for homeownership that is as wasteful, as unfair, and as harmful to the economy in the long run.