This is an obvious point, but I think it’s worth mentioning. Immigration has many possible benefits (economic, social, national security, domestic security, and liberty benefits) and many possible costs (economic, social, national security, domestic security, liberty, and congestion costs). These benefits and costs vary by type of immigrant — well-educated vs. uneducated, rich vs. poor, single vs. family, old vs. young, from countries in which there is a substantial amount of militant hostility against the U.S. vs. from other countries, and so on — often in complex ways. Unless one believes there is a categorical moral duty to allow in all immigrants, something that to my knowledge only a few people believe, one must consider all these costs and benefits in deciding on immigration policy. That applies both to the decisions about who may lawfully enter, from where, and on what terms, and to decisions about whether we should allow some who have come or stayed illegally to become legal.
And these benefits and costs also vary by our legal and political system’s reaction to the immigration. For instance, the more medical, educational, and welfare benefits are available to immigrants, especially as soon as they arrive, the higher the costs, and the higher the risk that we will draw people who are less productive and more interested in those benefits (though it’s possible there may also be countervailing benefits as well). The more willing we are to deport noncitizens who commit crime, the lower the likely domestic security costs of immigration (keeping in mind that there might always be perverse effects that one might miss in the initial cost-benefit analysis).
This is particularly true of liberty costs. If letting in immigrants leaves us as free as we ever were, that’s great. But the more it means our liberty must be restricted to accommodate immigrants — and even their descendants — the more we should worry about immigration, especially since we should rightly value liberty highly. The California high school officials who sent kids home for wearing an American flag (incidentally, kids whose names suggest that they themselves are likely the descendants of relatively recent immigrants) was essentially concluding that immigration imposes substantial liberty costs, as well as domestic security costs (since the justification was a fear that the American flag T-shirts might provoke an attack, presumably by those who supported the Cinco de Mayo celebration).
If the school officials are right, then that’s an argument against allowing more immigration. And whether or not the school officials are right, if their actions become common, those actions themselves would become an argument against allowing more immigration. And this is so even though the consequent reduction in immigration will end up being overwhelmingly borne by people who are law-abiding, and who have no desire to reduce the liberties of American citizens.
On the other hand, the more our system welcomes new immigrants but at the same time assures citizens (many of whom might themselves be immigrants or children of immigrants) that their liberty will not be reduced as a result of the immigration — and that the government is prepared to take measures to reduce the other costs of immigration, too — the more open American citizens ought to be more immigration.
(By the way, I recognize that some Hispanics in California are the descendants not of immigrants to the U.S. but of Hispanics who were already living here when the U.S. acquired California and other states from Mexico following the Mexican-American War. But my sense is that this is a very small part of the Hispanic population.)