One thing that strikes me about libertarians who oppose open borders is that they approach the issue of immigration completely different from how libertarians approach nearly every other issue. Arguments against immigration typically go as follows:

Bad effect x will happen if we allow open borders. Therefore, the government is justified in restricting immigration.

For example, many libertarians claim that because immigrants will increase deficits by using the welfare state, the government is justified in restricting immigration. Of course, this isn’t actually true, but even if it were true this in no way justifies immigration restrictions.

To be clear: immigration restrictions are a form of government intrusion into an individual’s freedom of movement. It is the government using its monopoly on force to restrict someone from doing something they’d otherwise be able to do, that is move across an arbitrary line we call a “border.” As Jason Brennan says:

At first glance, immigration restrictions look like rights violations. When we impose immigration restrictions, we do not simply fail to help would-be immigrants, but rather use violence and threats of violence to prevent them from making life-saving or life-changing trades with willing trading partners. We also harm our own citizens, who would benefit from interacting with those immigrants. We impose ourselves and cut off relationships that otherwise would have formed. We use violence and threats of violence to interfere with people who, if left alone, would work or live or trade together.

So libertarians who make this argument are substantially saying that if it can be shown to reduce deficits, using government force to restrict someone’s freedoms is justified.

If anti-open borders libertarians treated any other issue like they do immigration, it would lead to some pretty absurd, anti-libertarian policy positions. For an example, as long as we have government-provided Medicare programs, allowing people to eat unhealthy foods or smoke will increase the cost of those welfare programs; following the logic of the argument above, the government would be justified in implementing paternalist policies that restrict people’s right to consume what they want to reduce the burden of the welfare state. People with lower incomes are more likely to use welfare programs as well, so the government is justified in reducing their population size by restricting their right to reproduce through forced sterilization.

Obviously, both these positions are absurd from a libertarian perspective. Someone’s freedom from government force in areas of reproduction and what food they consume is more important than the fiscal costs. What makes the freedom of movement any different? Replace “people with lower incomes” with “immigrants” and “sterilization programs” with “immigration restrictions” in the sentence above, and the argument is the same. If the government cannot restrict freedoms in other areas in the name of deficit reduction, what makes freedom of movement in immigration restrictions any different?

Or take another example, many libertarians justify restricting immigration because immigrants are likely to vote for statist policies that will restrict liberty. Of course, this once again isn’t true, but even if it were it by itself is no reason for libertarians to support immigration restrictions. The operating principle here is that government is justified in restricting individual liberty if it increases the likelihood that pro-liberty politicians will be elected.

Again, that principle is not applied to any other issue by libertarians. Let’s say a particular demographic of citizens is more likely to vote for statist policies; by this argument, the government would be justified in reducing their population through sterilization programs in order to increase the likelihood that libertarians would win elections. Citizens who vocally advocate for statist policies through their speech also increase the likelihood that people will vote for those statist policies, so the government would be justified in restricting their freedom of speech. Obviously, both conclusions are absurd.

Further, as Bryan Caplan argues, it must be shown that there are policies that can reduce these ill-effects while violating fewer liberties than an all-out closed border policy. For example, we can eliminate the welfare cost of immigration by allowing for an open borders policy but make it illegal for any immigrant to receive welfare benefits. This allows for freedom of movement but eliminates the alleged ill-effect of open borders. Additionally, there are undisputable benefits from immigration, both in terms of increased liberty of movement and economic growth, and it must be shown that the negative effects outweigh the positive effects. Therefore, premise 2 is also incomplete as stated above.

So, in reality, these types of arguments against immigration are as follows:

1a. The government is justified in restricting someone’s liberties if it can be shown to stop bad effect x.

2a. X will happen if we allow for freedom of movement through immigration and there is no other way to stop x without restricting freedom of movement.

3a. Therefore, the government is justified in restricting immigration.

In reality, very few libertarians accept 1a, particularly if they believe in deontological natural rights. For consequentialists, it would depend on how bad x is. But for most arguments against open borders, they would not say that x is bad enough to allow for restrictions on nearly any other liberty. Further, as pointed out earlier, premise 2a is usually false because the empirical evidence suggests that x will not be a result of open borders, there is some other way to stop x while allowing for free migration, or both.

Another argument is that there is something distinctive about immigrants that justifies the state violating their rights but not citizens. If this is the case then we can replace 1a above with the following argument:

1b. The government is justified in restricting the rights of non-citizens if it can be shown to stop bad effect x, but would not be justified in violating the rights of citizens even if it would stop x.

This isn’t really a premise, but a conclusion; libertarians must justify some argument for why it can restrict the rights of non-citizens but not citizens. On its face, it seems like this principle is pretty absurd. For example, suppose that Greek citizens who use welfare eat unhealthily, and this is harming Germany fiscally because Germany helped bail out the Greek welfare state. The German government, therefore, passes a law restricting what Greek citizens can eat and tried to enforce it on Greek soil. Clearly, nobody, libertarian or otherwise, would call that justified. It is the burden of proof for open borders opponents, then, to prove why citizenship is in any way morally relevant to restricting liberties.

Perhaps there is an argument for why someone’s rights are all of a sudden less valuable because they were born on the wrong side of an arbitrary line that only exists because of state force. However, I doubt that there is such an argument that is in any way consistent with libertarian philosophy.