Free immigration, also known as free labor mobility, is likely to have the following effects (the effects are all interlinked):

• Double world GDP:World GDP will experience a one-time boost of about 50-150%
• End of poverty: The GDP gains will be felt most by the world’s poorest, and absolute poverty will reduce dramatically.
• The master race: The (relatively) poor in the developed world may be moderately worse off in the short run. However, under any reasonable welfare comparison, this slight decline would be considerably smaller in magnitude than the gains to immigrants and the rest of the world.

For more on the practical details of the arguments, see:

• Benefits to migrants
• Benefits to immigrant-receiving countries
• Benefits to immigrant-sending countries
• Global benefits

What is utilitarianism?

Utilitarianism is a philosophy where the basis of action is to “maximize total utility” — it is the underlying idea behind cost-benefit analysis. A more general term is “consequentialism” which says that actions and decisions must be judged by means of their consequences. For more, see the Stanford Encyclopedia of Philosophy articles on The History of Utilitarianism and Consequentialism.

Why should the utilitarian case matter to non-utilitarians?

Few people are willing to embrace utilitarianism wholesale. However, it’s also true that, in cases where there are multiple courses of action each of which is morally permissible, people are comfortable using utilitarian methods such as cost-benefit analysis to figure out which course of action to take. Further, interesting paradoxes aside, in many cases, the morality of an action is partly determined by its consequences. This idea is utilitarian.

In the case of open borders, the utilitarian case for it is overwhelmingly strong. Combining with the fact that there is a strong libertarian and a strong egalitarian case for open borders, the overall argument becomes quite strong.

Objections to utilitarian case

Most of the objections to open borders, with the exception of objections to the libertarian case, are essentially objections to the utilitarian case. The way these objections typically work is that, rather than considering “total” utility, they focus on utility to a specific segment of the world population. Some objections focus on harms to immigrant-receiving countries, whereas others focus on harms to immigrant-sending countries. There are some objections that focus on global harms.