Immigration restrictionists argue that allowing lots of newcomers into the United States imposes costs on Americans. Admit it, my pro-immigration colleagues, the restrictionists are right: setting aside the question of whether immigration is a net benefit to the United States, it is clear that newcomers lower the wages of Americans without a college degree, pose certain public health risks depending on their country of origin, require public schools to hire costly bilingual educators, and otherwise impose costs on some citizens. High levels of immigration benefits some Americans. But the benefits are dispersed unevenly, and it produces losers too.
The argument I want to raise today is that even if you're among the net losers, you have a moral imperative to favor permitting lots of new immigrants to enter America legally, because at some point in the past, your ancestors arrived here from somewhere, and on doing so they imposed costs on the people already here. It is hardly fair, now that you've reaped the benefits of past immigration, to restrict others from doing the same.
This argument is particularly compelling because odds are when your ancestors came to this country, the burdens their arrival imposed on the folks already here was many times greater than anything you'll face today. The Europeans who initially came to this continent spread diseases that wiped out Native American populations -- and the ones who survived disease were often kicked off their land or even brutally killed. Folks of Irish ancestry who complain that their cities are overcrowded today should read about New York City tenements during the biggest wave of immigration from Ireland. Are you worried about immigrant gangs like MS13? So am I, but it's doubtful that any imported criminal organization will prove more burdensome than the Italian mafia or the organized crime families that exist in many other ethnic groups that immigrated to the United States.
Name any problem associated with immigration today, and odds are it was much worse at some point in the American past -- and our ancestors grappled with those problems despite living in a country many times poorer than the America of today. Unless you're a Native American, fairness would seem to demand that you don't favor restrictionist immigration policies that, were they in place when your ancestors came, would've prevented their arrival and your status as an American today.
(Note that this argument says nothing about the illegal immigration debate -- it is an argument that everyone should support high levels of legal immigration.)