The Mercatus Center held a book forum on In Defense of Openness (IDoO) with Anna Stilz, Kit Wellman, and James Witte as respondents. I'll post the podcast when available.
Our main strategy in the first few chapters of IDoO is to argue that there is an extremely strong presumption in favor of free trade and open borders. We then look at and defeat objections which try to override this presumption.
We start by using modification of Michael Huemer's starvin' Marvin case, which goes roughly as follows:
Imagine Starvin' Marvin is starving. He will starve unless he makes a trade with some people. Fortunately, there are people in a market who want to buy what he sells. But suppose Bob shows up with armed guards and forbids those people and Marvin from trading. As a result, Marvin dies.
Here it looks like you have done something really evil and wrong. You don't have to be a libertarian to agree.
In response, Stilz said:
For one thing, the case is ambiguous: it’s not obvious that what is salient here is that Marvin is prevented from making a trade with a willing partner, rather than the fact that he is placed into a scenario in which he must starve and die. Most people agree that it is wrong to leave people with no option but to starve. But note that there are many ways to prevent starvation (we might give people a right to economic exchange, we might give them a universal basic income, we might give them land on which to grow food, and so on). So how do our intuitions about starvation support strong rights of free exchange?
That's right on it's own as a response to this one example, but it's a problematic response overall for a few reasons.
1. We anticipated this point in the book. Accordingly, we included number of alternative cases where the stakes are lower. It still seems wrong, indeed, awful and rotten, to interfere even if the stakes are lower. Imagine Marvin will merely remain poor. Or imagine Bas is literally indifferent between eating at Denny's or Perkins, but I show up with a gun and order him to pick Perkins. Here, I have treated Bas very wrongly, even though he is indifferent between the two outcomes. The wrong of interference comes not merely the welfare loses from interference, but from the interference itself. We don't even have to posit that Bas has a "right to choose where to eat" to explain why this such an evil way to treat him.
Indeed, if you have a theory which says, "When Bas is indifferent between A and B, it's ok to threaten to force him to choose B with state violence," I'd regard that as a reductio of your theory. The fact that your theory says that means your theory is false. (If you had some good reason to threaten him, that's different, but it'd better be a mean good reason. See below.)
2. Regarding Stilz's own solution, imagine that when Starvin' Marvin shows up, I once again post armed guards and forbid him from making a willing, consensual, mutually beneficial trade with others. But suppose I offer him a sandwich and care package, plus I give the willing trading partners some cash, too. Here, it nevertheless seems that I wrong him badly. Threatening him with armed guards and violently stopping adults from interacting with each other who want to do so seems very wrong, even if I make the payments so high as to be equal to the welfare gains from trade. I had better have a damn good reason for treating them this way. Not just any old reason will do.
It's of course scary and frightening to have armed guards who threaten people with violence. This is more analogous to the real world--there are indeed armed men who will attack you at the border or track you down and attack you inside the country. Indeed, even US citizens such as I have to interact with armed, mean Border Patrol agents when driving on various highways in the US. But you imagine that the interfaces is done magically instead. Suppose I cast a magic spell which simply prevents Bas from ever going to Perkins. He would rightly be pissed even though by hypothesis he has other alternatives that are as good.
So, there is a strong presumption in favor of not treating people like this. This presumption can be overridden or defeated if one can show that there are other hidden moral or welfare costs to allowing such trades, but the presumption must be overcome.
3. Overcoming the presumption is difficult, not easy, as Stilz suggests. Consider some things that would not justify this kind of violence or interference: You can't forbid Marvin from trading because you feel like it, because you dislike his race or religion, because he listens to the wrong music, because you want to use video footage for a documentary you're making, as a form of performance art, because some of the neighbors dislike it when people trade, or because some other people want to trade with Marvin's potential partners and hate the competition. You can't say, "I want to stop Marvin from trading because I am worried that it will reduce the income of the very rich by a slight amount for a short time." None of these look like good justifications. So the presumption seems very strong, not weak.
4. It's worth noting--and I did note--that even Rawls agrees. (Stilz is, I think, a kind of Rawlsian.) Rawls things there are very strong rights to be able to live where you want, to take a job you want (subject to reasonable regulation and licensing in special cases), and so on....but only within one country. But Rawls has close to zero argument at all for restricting this to one country.