Not really sure what to make of someone who responds to concerns about justice in housing with "solve for equilibrium hero derp." I'm pretty sure that Nathan wasn't suggesting that everyone be given a 3k square foot McMansion with a four-car garage in the exurbs. The notion that the United States can't afford, say, some kind of social housing guarantee (or any of an array of reforms to federal housing policy to make it more fair, pro-social, and sustainable) is laughable.
(And, if you're really concerned about efficiency, it would probably cost less than the home mortgage deduction!)
Housing policy is something of a side-interest/passion of mine. I don't think Castro has done a terrible job given the status of the market as it exists today, and these people are not being particularly fair to him, but there is space on the left for some bold housing reform because it really is a messed up, unfair, inefficient, environmentally unsustainable and unjust. I just don't think the job of HUD Sexretary is where you make that change from. It has to be much, much bigger than that.