One of the things that puzzles me about immigration restrictionists is how minor the harms they think they need to establish from immigration to overcome the moral presumption in favor of immigration. Even for those who don’t have sympathy for the libertarian and egalitarian arguments for open borders, there remains an extremely strong utilitarian case for open borders, which includes the doubling of world GDP and the end of poverty.

One explanation for restrictionists’ reluctance to concede the strong utilitarian case is that there are various philosophical bases for anti-immigration arguments such as citizenism, territorialism, local inequality aversion, and nation as family, which fundamentally reject universalist morality and favor the interests of specific individuals.

In a blog post comment on EconLog, Evan offers a somewhat different explanation:

I don’t know what Bryan will argue, but I think you could make a good case by using “shut up and multiply” type arguments. I.E., immigration restrictions are such a horrible violation of ethics and liberty that they’re worth putting up with other violations in order to stop them.

I personally know that if I had a choice between the USA as it currently is, or a USA with no welfare state, but closed borders between states or counties, I’d pick the status quo. In fact, if I was forced to choose between doubling the size of the welfare state, or closed borders between states and counties, I’d probably pick the former. That indicates to me that closed borders are a monstrous injustice, and the only reason people don’t realize it is scope insensitivity, or by being lucky enough to not have personally been harmed by them.

Here’s a quick summary of scope insensitivity from this page:

Once upon a time, three groups of subjects were asked how much they would pay to save 2000 / 20000 / 200000 migrating birds from drowning in uncovered oil ponds. The groups respectively answered $80, $78, and $88 [1]. This is scope insensitivity or scope neglect: the number of birds saved – the scope of the altruistic action – had little effect on willingness to pay.

Is Evan on to something? I don’t know. I suspect that scope insensitivity is a real phenomenon in immigration debates, but restrictionists are often quick to point out numbers when it comes to talking about natives hurt by immigration. So, my best guess is that restrictionists employ selective scope insensitivity. Another possibility is that they are using the logic in Roy Beck’s gumball video to dismiss the gains from open borders.