Immigration of the right kind is a great benefit to a nation run under principles of liberty. If the immigrants obey our laws and work productively, they will add to the nation’s wealth. If they assimilate to the nation’s creed of liberty under law, they strengthen its power throughout the world, because their former compatriots take heed of their success and that example may encourage more liberty in their home nations. And not only do the citizens of the welcoming nation benefit, so also do immigrants. The value of their human capital rises as soon as they set foot in a nation of free markets and the rule of law.
The way to encourage citizens to embrace immigration from abroad is to have a constitution that limits welfare programs and precludes ethnic discrimination. Without such commitments, citizens may rationally worry that poor and even work-shy immigrants may come and eventually vote themselves higher levels of benefits, even at the expense of long-time citizens and their descendants. Without guarantees against discrimination, citizens may also worry that ethnic groups who still feel solidarity based on previous ties, will try to organize government benefits on the basis of ethnicity, impeding assimilation.
And now I can reveal that once there was a nation that had a constitution with the pre-commitments needed to facilitate a sound immigration policy. It was the United States after it had ratified the 14th Amendment.