Some serious evil is done when people who have lived peacefully and productively in any country for a long time are coerced to leave just because they came there illegally or overstayed a temporary visa. Joseph Carens writes wisely about that. But the evil in what he deplores is not enough to justify making all such people eligible for permanent residence once they have evaded arrest and deportation for a few years. Carens is too cavalier about how such an indulgent policy could be justified in real-world circumstances. With all things considered, we might find ourselves having to choose between competing evils in designing laws to cope with illegal immigration.

Suppose the United States adopts Carens’s proposal. Might that boost the number of poor people entering the country illegally? The staggering scale of illegal immigration since the mid-1990s and until very recently should give us pause. The United States now hosts about eleven million people who are in the country illegally, and a large portion of this group seems to want to stay. Many already have spouses or children who are legal residents or citizens. Some might be ready to go back home, at least for a while, if returning here were not so perilous. But the very fact that people are deterred from going home because they might want to get back into the United States at a later date suggests that the possibility of legal permanent residence in the United States would be alluring to them. And surely relatives and fellow villagers in rural Mexico, say, will also be very interested to learn that secure permanent residence could be theirs after only a few years of enduring the anxiety and exploitation that working illegally entails. No one could blame them if new hopes drew them here.

If poor people want to enter a rich country because they hope for a better life, why should we care? The most familiar answers to that question have a disturbingly chauvinistic tenor. But one answer has nothing to do with chauvinism. It argues that numbers matter: the value of legal permanent residence to those who have it erodes as the scale and political intractability of poverty among them escalates. The United States is a case in point.

The American dream has been a hoax for many to whom it was promised. An opportunity to escape poverty through sheer hard work has always been out of reach for millions trapped in a caste-like social status. Intergenerational poverty among Americans of Mexican origin or ancestry is already a problem of shocking proportions. Most Hispanic residents of this country could well evolve into a huge pariah category, largely consigned to ill-paid work from one generation to the next, with negligible access to decent educational opportunities and other social benefits, and largely excluded from the centers of social power. Some social scientists say that this has already occurred. The more optimistic ones say that Hispanic Americans are merely on a slower path to integration than others, though the optimists are quick to add that much better schools for everyone and other improvements to America’s shabby welfare state are necessary to secure that happy outcome. If these are necessary, and if illegal immigration spikes yet again, we could be in even more trouble than we are now.

The trouble starts with an American electorate that has long been very tolerant of widespread poverty among their compatriots. Americans seem to believe that all fellow citizens or permanent residents should get a fair shot at the American dream. But that article of civic faith coincides with widespread aversion to the costs of any social policy that would stray much from what citizens perceive as their material self-interest. And so political strategies that can improve opportunities for the poor have to combine a high-minded civic rhetoric with assurances that high-mindedness will not cost taxpayers much.

If the American dream is ever to be available for the millions of Americans now excluded, we must adapt progressive political ends to the priorities of people who worry about what is in it for them. To ask such people to extend help to poor compatriots when those compatriots are within the predictable control of the state, and domestic poverty is a problem with tolerably clear boundaries, is one thing. It is quite another to do so when “permanent legal resident” becomes as easily acquired a status as Carens’s proposal would make it and as the number of illegal immigrants swells in the hope that the American dream might be available to them, or at least their children.

The hard truth is that immigration policies in the United States that are hospitable to the wretched of the earth may come at some cost to the likelihood that Americans will ever be mobilized to do much about the wretched already in their midst.