We think the freedom to immigrate is a basic liberty along with freedom of speech, freedom of conscience, occupational freedom, and so on. A truly liberal state would respect all of these liberties. But not everyone believes that the freedom to immigrate is a basic liberty.
David Miller argues that some freedom of movement is a basic human right because it is needed to protect vital interests. If you’re locked in a cell, you lack the freedom of movement you need to live a decent life. But you can live a pretty good life without unlimited (or close to unlimited) freedom of movement across borders.
But, if people are only entitled to adequate freedom of movement, then why aren’t they only entitled to adequate freedom of speech or religion? (For similar objections, see Oberman, Brezger & Cassee, and Hidalgo). Surely you can still live a pretty good life if the state prevents you from practicing your religion between 2-3AM on the first Tuesday of each month. The same goes for having 2 or 3 children rather than 7. And you don’t really need all those books on gluten-free cooking, do you? Nevertheless, no liberal thinks the state is justified in restricting freedom of religion, reproductive choice, or freedom of the press in the preceding ways, at least not without extraordinary reasons.
Miller has a reply: empowering the state to restrict freedom of religion (for example) is more likely to lead to abuse and oppression than empowering it to restrict freedom of immigration. Suppose he’s right. This distinction still wouldn’t explain why it is wrong for the state to restrict liberal freedoms like freedom of religion. To see why, just imagine that we live in a country with a “Unicorn State” that never abuses its power. So, for instance, if that state passes a law that prevents you from, e.g., practicing Calvinism between 2-3AM on the first Tuesday of each month, there is no danger of this power spilling over into other cases. Still, this is a bad law–people ought to be allowed to practice Calvinism between 2-3AM on the first Tuesday of each month. The takeaway point is that a state that respects only those liberties needed to protect vital interests is insufficiently liberal. So even if an expansive freedom of immigration isn’t needed to protect people’s vital interests, it may still be the case that such an expansive freedom ought to be respected.
Think about it this way. Even if the right to immigrate isn’t as important as other liberties on average, it can be more important on the margin. Consider two scenarios. In scenario 1, the government forbids Chris and Javier from practicing Pastafarianism. In scenario 2, the government prohibits Chris and Javier from moving to California. We each have good lives in Virginia and we don’t have any plans to move to California. But we would be more upset in scenario 2 than in scenario 1. This suggests that freedom of movement is sometimes even more important than other basic liberties.