A. The US admits 1 million immigrants per year between now and 2050.
B. The US admits 3 million immigrants per year between now and 2050.
Suppose we only cared about the welfare of Americans. Would Americans be better off in 2050 under policy regime A or policy regime B?
Surprisingly, the answer may well be "yes." That is, whichever policy option is adopted will make Americans better off (as compared to the alternative policy.) Given how inept our policymakers are, thank God for that!
At first glance my claim might seem like a logical contradiction. The trick (or gimmick) is that the term 'Americans' means something very different in policy A as compared to policy B. More specifically, policy B will result in lots of people counting as "Americans" in 2050 who (by assumption) would not count if policy A were adopted.
The Scandinavians, in contrast, spend a heck of a lot of money to see to it that migrants can be full participants in society. They don't always do a great job, but they certainly try. And they try because they reject the idea of a two-tiered society, in which privileged natives live cheek-by-jowl with migrants who have no hope of living alongside them as equals. Perhaps the Scandinavians are just naive. If these migrants weren't living alongside them, they'd still be living somewhere, and they'd almost certainly be a lot worse off. Other views, however, are that migration can never be as good a solution for fighting global poverty as improving governance in poor countries and that all countries, including rich countries, have the right to pursue their vision of the good society--including one in which you accept a small number of migrants and treat them extremely well.
I find it interesting to see a conservative make this argument, because I believe it underlies much of modern progressive thought. As an example, it's pretty obvious from the intense reaction to Thomas Piketty's new book that the progressive movement is currently more focused on the "cheek-by-jowl" inequality that blights New York, Miami and LA, than the (diminishing) inequality between the incomes of Iowa farmers and Punjabi farmers.
Keynes spoke of poverty as being "ugly," and I think that's right, but primarily a certain type of poverty. Poverty juxtaposed with wealth. That grates on our sense of fairness, especially where the poor are obviously trying very hard (say California farm workers.) If you are a nationalistic conservative, you might not be bothered by income inequality, but might find cultural diversity to be distasteful.
I don't intend to preach a message on immigration here, but rather I'd like to warn against cognitive biases. When thinking about what's best for America in 2050 we need to think very hard about whether we are interested in the well-being of people living in America in 2050, or the well-being of those people currently living in America (and their children) who are still alive in 2050. That slight change of focus can lead to radically different policy implications.
Utilitarians like me and non-utilitarians like Bryan Caplan are very interested in the welfare of anyone who might be living in America under various possible policy regimes. Many progressives put a lot of weight on the welfare of illegal immigrants who live in America today, but much less weight on the poor in other countries who do not live "cheek-by-jowl" with affluent native-born Americans. Some conservatives put much less weight on the welfare of illegal immigrants than they do on the welfare of those who are in America lawfully. Or perhaps they put more weight on rules than outcomes.
Conservatives should not forget that we can also play this game by running the clock backwards. From the perspective of Native Americans, most European Americans are "illegal immigrants." And European immigration probably made Native Americans worse off. Before Columbus, the natives of North America often had relatively good health, based on average height. Today many live in failed communities full of crime, poverty and alcoholism. A large portion died of diseases like smallpox soon after the Europeans settled America. [Yes, their descendants now have cell phones, but surely there is more to life than technology.]
From a global (utilitarian) perspective, the discovery of America was clearly a good thing. It increased global population and wealth dramatically. If America had not been discovered, hundreds of millions (maybe billions) of people would not be alive today. Nonetheless, the result was surely not anyone's "vision of the good society" for Native Americans, to use Salam's terminology. And the Native Americans of 1491 were the only Americans whose welfare should have "counted," according to one popular view of national self-interest.
To conclude, when thinking about immigration it depends very much on how you frame the issues. Who counts and who doesn't count? Do we add up the welfare of 7 billion individuals, or construct an aesthetically pleasing "good society" in our small corner of the planet?
I'm a bit more agnostic on these issues than Bryan, but you can probably tell which way I lean, at least at the margin.