The point of our paper is this: If you are going to take [utilitarian] philosophy seriously, you have to take all of the implications seriously. And one of those implications is the optimality of taxing height and other exogenous personal characteristics correlated with income-producing abilities. A moral and political philosophy is not like a smorgasbord, where you get to pick and choose the offerings you like and leave the others behind without explanation.
There are plenty of small things to say about this. Height is not perfectly exogenous -- we can imagine people trying to reduce their height to reduce their tax burden, can't we? -- and the fact that the correlation is not perfect suggests there will be some individuals unfairly affected by a height tax. (On the other hand, as the government's information gets better we could imagine that unfairness disappearing.) But mostly, I want to say this: Isn't moral and political philosophy exactly like a smorgasbord?
Consider everyone's favorite hypothetical from ethics 101: A runaway train is barreling down the tracks toward five workers, unaware that they're in for a grisly demise. You are standing on a bluff overlooking the scene, in front of a magic lever that can divert the train to a separate track on which there is a lone worker. Do you pull the switch?
It seems intuitively obvious to me, and I think intuitively obvious to most people, that you should pull the switch. But for me that intuition does not hold across all cases with similar stakes. Switch the scene to a hospital emergency room in which you are the surgeon. You have five patients desperately in need of organ transplants. In walks a healthy person. Do you whack him over the head with a mallet and harvest his organs to save the other five? Maybe readers of the Atlantic aren't so cowardly, but I wouldn't!
But I don't really have a good explanation for why I wouldn't, except that intuition tells me I don't want to live in a world where doctors can whack me over the head and steal my liver and lungs in the name of the greater good. Of course, I'm perfectly OK with being run over by a train for the same principle. But the blatant hypocrisy of this really doesn't keep me up at night, largely because I don't see the alternative: Everyone has moral intuitions they can't justify in the same we can justify the pythagorean theorem, and I don't see the point of fighting that strong impulse in the name of a hobgoblin-ish consistency.
So I think of height as a little like the hospital. I have a strong moral intuition -- even though I know it's one I can't justify -- that height is something I deserve. But proving that my moral intuitions are an inconsistent smorgasbord doesn't mean I'm going to give them up!
(Note Bene: This is getting somewhat far afield of the original tax question, but I wouldn't pick the utilitarian social welfare function, either. A Rawlsian social welfare function -- attempting to maximize the the utility of the least well off person within some other constraints -- strikes me as a better alternative. I am assuming that Mankiw's argument for a height tax holds for a Rawlsian social welfare function too. But it's possible the height tax would violate some other Rawlsian principle -- like the principle of greatest equal liberty. Maybe some moral or political philosophers would have an opinion on that.)
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