Matthew Stewart’s new Atlantic article on some pervasive and under-appreciated sources of American income inequality is an absolute must-read for two reasons – the first obvious and critical for the long-term; the second less obvious but critical for the short-term.

The obvious reason is Stewart’s focus on how America’s affluent “meritocrats” – not the super-duper wealthy, but the roughly 10 percent of the population just below them on the income ladder, who fill the nation’s professional ranks – are greatly widening the gap between rich and poor by various behaviors that pass all of their advantages down to their children.

This pattern, and its principal origins, aren’t news to anyone who closely follows inequality issues and the research they’ve generated. But Stewart makes a major contribution to public understanding by insightfully describing how the main trends responsible – like the growing tendency of this “9.9 percent” to educate their kids in ways that typically send them to elite colleges and universities, where they marry each other and produce offspring likely to repeat the pattern – mark this cohort’s lives thoroughly enough, both economically and in social and cultural outlooks, to blind its members to the devastating consequences for the less fortunate.

Even more important, since the results are so easy to view as the products of a natural selection process in which the “best and the brightest” receive their deserved rewards, even the most avowedly progressive of these “new meritocrats,” rarely think about public policy measures that can level the playing field, let alone actively support their development and approval by politicians.

At the same time, this particular supertanker of a development, and the widening inequality it’s fostering, isn’t going to be turned around easily, even if the optimal policies were put in place tomorrow. Of more immediate interest is the second, less obvious aspect of Stewart’s article: all the data he spotlights now showing so conclusively how social mobility is disappearing from the United States. In other words, not only is the nation becoming more unequal, but it’s gotten excruciatingly difficult for lower-income Americans to advance into middle-class ranks and beyond.

Greatly reduced social mobility matters so much right now because, as I’ve written previously (e.g., here), it completely shreds one of the main economic arguments made in favor of more lenient immigration policies: the claim that the population growth generated by encouraging the arrival of more newcomers from abroad, regardless of their current income and education levels, is vital to ensuring continued U.S. economic growth and prosperity.

In a country in which social mobility remained high, such policies would arguably make sense. But in a country in which anyone lacking impressive education and incomes is almost guaranteed to stay uneducated and poor, and ditto for their children, they become completely ridiculous. In the case of many immigrants coming in through family unification programs and the visa lottery, not to mention amnesty for most of the illegal immigrants already present, the result would by and large be a major importation of – persistent – poverty, an acceptance of a largely impoverished population that should have been kept out in the first place, and a consequent strengthening of the magnet sure to attract even more individuals who (through no fault of their own) seem destined to become economic drags.

So here’s hoping that American leaders on both sides of the aisle read Stewart’s article all the way through – and that the Open Borders crowd in both Democratic and Republican ranks gets the message that the author is sending unintentionally as well as the one he’s clearly, and rightly, hoping to convey.