Gallup estimates that the US population could surge by 180 Million if everyone who expressed a desire to move to the United States did so. Indeed, the number would likely be higher as in Gallup’s hypothetical asked for first choices and presumably the United States is the second choice of many potential immigrants.
So far most anti-immigration folks have expressed the most concern over Hispanic influx. Perhaps, they would be comforted to know that most would be Americans are Asian.
In any case immigration is the most important policy facing the United States over the medium term.
First, an increase in immigration permanently dilutes the costs of military action. Military expenditures are invariant to the population. Yet, over the long term this is actually a much larger concern than either Social Security or Medicare. As China, India and Brazil industrialize, either the United States will have to drastically increase the percentage of GDP spent on the military or it will have to relinquish its position as a world superpower.
I know that seems like a fine idea to many, especially to many libertarian minded folks. However, liberal democracy has flourished almost entirely under the canopy of Anglo-American hegemony. It is entirely possible that a truly multi-polar world could sustain liberalism but it is not, however, entirely certain. To my mind the maintenance of the Open Society is our primary responsibility and I am not inclined to leave it to chance.
Now let me be clear. I am not an evangelical liberal. I don’t see it as necessary or even in all cases desirable to attempt to spread the basic principles of the Open Society. I do see it, however, as crucial to maintain the Open Society where it currently exists.
Second, immigration temporarily dilutes expenditures on Social Security, Medicare, and interest on the national debt. However, temporary counts for a lot. The future is inherently uncertain and so truly pushing off consequences into the future is inherently a net gain. There is a chance of catastrophe, in which case your sacrifices were useless and there is a chance of explosive growth, in which case your sacrifices were unnecessary. These are real possibilities and should not be ignored.
It also gives additional time to prepare for changes in Social Security. One possibility is that the continued shift away from physically intensive jobs will mean that in 50 years a retirement age of 70 is feasible even if in 25 years it is not.
In addition, it gives more time for changes in the medical industry. Our current projections for Medicare are based on the assumption that medicine will experience excess cost growth indefinitely. Obviously, this is impossible. Something will happen which slows the growth of medical spending. Stretched far enough into future the cost curve has to bend. If for no other reason then because eventually medicine will be 95% of GDP and thus the two growth rates will be essentially identical.
Third, the rate of world wide technological progress is likely proportional to the number of people living in countries at or near the technological frontier. Increasing the number of Americans increases the growth of technology generally.
Fourth, immigration is the most effective poverty elimination program known. Not only does it dramatically increase the standard of living of the immigrants but remittances to home countries by immigrants represents a greater transfer of resources than all foreign aid combined.
UPDATE: Conor Friedersorf adds the guilt angle