Ross Levatter at libertarianism.org attempts but fails to take me to task for asking the following question:

Imagine that a bunch of economists provide compelling evidence that life in a strictly libertarian polity would be a disaster. Imagine that they show conclusively that if people everywhere were to live in a Nozickian minimal state or a Rothbardian anarcho-capitalist civil society, with everyone strictly observing property right rules, that 10% of people would starve, 80% would be near subsistence, and only 10% would prosper.   [Imagine also that a more socialist political economy functioned far better.] …what would you advocate and why?  [Would you still advocate libertarian politics?]

Levatter thinks this thought experiment comes perilously close to asking people to imagine square circles:

Here’s the problem: The economic counterfactual on which Brennan bases his thought experiment is not like “Imagine demand for X is inelastic³ rather than elastic”. It is more like, “Imagine demand curves slope upward⁴ rather than downward for all goods over all ranges. Then what?!” Such thought experiments, based on such a gross and fundamental divorce from all empirical economic knowledge we have ever experienced, give us little guidance, just as (even though biology, too, is an empirical science) a thought experiment involving the immortality of wizards would give us little insight into appropriate ethical action in our world…

…Presumably no one, including Brennan and Zwolinski, really believes they know of any historical instance where what traditional libertarians desire has been closely approximated and yielded anything remotely close to the results of their thought experiments. Is it fair to describe their pure thought experiments as divorced from real world experience in a very fundamental way, deeply impossible in Parfit’s sense?

My most charitable guess is that Levatter is just widely misinformed about the state of economics. So let’s be clear:

1. Libertarianism does not follow, as a matter of logic, from fundamental economic principles that no reasonable economist could challenge.
2. Behavioral economics might cast serious doubt upon many basic assumptions in economics. It might turn out that economics is too a priori, and has little to say about the actual world. It might turn out that market actors tend to be highly irrational, that they do not correct their actions, and so the market does not function much at all like how micro textbooks, let alone Austrian books, say it does. It might also turn out that alternative economic systems, or more statist economic systems, better function in light of human irrationality. (Yes, perhaps it’s possible to correct gross human irrationality through government action. That’s not incoherent. “If market actors are irrational, then bureaucrats will be too” is too facile a response. You need actual evidence here to argue either way.)
3. It’s at least logically possible that market failures outweigh government failures significantly, and this calls for more government intervention and less freedom in markets.
4. Get out your micro and macro textbooks and look at all the controversial stuff in the back chapters. It’s possible that some form of Keynesianism is true. It’s possible that private charity works horribly compared to government social insurance. It’s possible that markets tend to have massive failures and problems unless corrected by government. Etc.
5. It might turn out that, say, the libertarian view of the war on drugs is wrong. It’s at least logically possible that legalizing drugs would cause worse problems than keeping them illegal, especially if the drug war were fought a different way.
6. It might turn out that, say, immigrants really do commit more crime, depress native wages, etc. They don’t, but we didn’t know for sure until we checked. And it may yet turn out that the extant research is mistaken.

And so on. Libertarianism doesn’t follow from fundamental principles or axioms that are not open to question. Rather, to get to libertarianism, if you are at all sensitive to consequences, you need to make a series of empirical arguments about how institutions work. Now, in light of existing social science, it’s pretty clear that large-scale economies need to be run fundamentally on market principles. But it’s highly controversial to what extent government should supplement, enhance, regulate, or supplant markets in order to generate what consequence-sensitive libertarians would themselves agree are better outcomes.

Now, Levatter might dispute 2-6. Perhaps he is right to do so. But if he’s not a crazy ideologue, if he’s at all informed about the state of the literature, he has to admit that 2-6 might be true, and that it’s easy to imagine a world much like ours in which they were true. If certain facts about human psychology had been slightly different, for instance, then the case for more government and less markets would be much stronger. If Ross thinks that, say, Robert Frank’s view of the economy is crazy* and easily dismissed as the view that demand curves slope downward, then that just shows Levatter doesn’t know what he’s talking about.

Levatter offers a thought experiment of his own:

But what about this unrealistic thought experiment?

In a re-write of the Harry Potter series, wizards are essentially immortal, such that no matter how completely and thoroughly they are killed, they pop back into existence a few seconds later no worse for wear. In this world, how evil was Voldemort for killing Professor Snape?

In such a world, killing a wizard is much like scratching his hand without his permission. Do we have strong ethical intuitions that Voldemort’s actions are evil in such a world, where killing Harry’s parents amounted to much ado about nothing? Even though our intuitions here suggest that wizard murder may not be such a big deal in that world, is there anything we can reasonably thereby conclude about murder in our Muggle world?

Actually, this is a great thought experiment, and philosophers who write about death often use thought experiments like this. It’s great because it helps us to isolate just what it is about death that’s supposed to be so bad.

Levatter complains about his thought experiment:

a thought experiment involving the immortality of wizards would give us little insight into appropriate ethical action in our world.

Well, it might or it might not. We don’t know until we see the final product, what the philosopher does with the thought experiment. It might be that the thought experiment ends up illustrating precisely what is bad about death, and so this helps us think through the problematic real-life cases and controversies, such as abortion, euthanasia, infanticide of deeply disable and ill infants, eat meat, and so on. Or it might not. Levatter didn’t try to do anything with this thought experiment, so he’s not in a position to tell us it will tell us nothing. He should instead see what such a thought experiment might do in the capable hands of, say, Shelly Kagan.

Even if it didn’t provide us any practical guidance for the real world, given the facts that obtain here, that might not matter, either. Moral and political philosophy is not all or even primarily about providing an algorithm to tell people what to do here and now.
*P.S. Yes, Frank strawmans the other side incessantly in The Darwin Economy. But that doesn’t mean that Frank’s positive defense of his position is mistaken.