Dylan Matthews records Bryan Caplan making a very persuasive case for open borders. One of Caplan’s best arguments is the entrance of women into the workforce in the 60s, 70s and 80s. “Was the result mass unemployment for men, as women took all their jobs? Of course not.” But that frames it in the negative. Does anyone doubt that the American economy is better off because women can work? Of course not. Even the most retrograde sexists base their arguments on culture rather than economics.

Does anyone doubt that the American economy is better off because women can work?

But a yet simpler metaphor is birth rates. Americans grok that higher birth rates are good for economies. Japan’s low birth rate is routinely framed as a disaster for the country. “Japan: Death by Demographics?” reads a typical headline in the National Interest. The same goes for Europe. Here’s Forbes: “What’s Really Behind Europe’s Decline? It’s The Birth Rates, Stupid.” And for all the puffery of China’s economic model, no one ever suggests America adopt their one-child policy. Quite the opposite, in fact.

Fittingly, declines in the American birth rate are treated as emergencies. “Forget the debt ceiling. Forget the fiscal cliff, the sequestration cliff and the entitlement cliff,” wrote Jonathan Last in the Wall Street Journal. “Those are all just symptoms. What America really faces is a demographic cliff: The root cause of most of our problems is our declining fertility rate.”

But there’s an easy way to solve for a declining fertility rate: open the borders.

SAUL LOEB/AFP/Getty Images

It’s intuitive to Americans that the economy benefits when there are more people around to invent, produce, and purchase stuff. As such, public opinion in America overwhelmingly favors the idea that we should make more people. But that consensus quickly breaks down when the conversation turns to letting in more people.

There are good reasons for that. A higher birth rate has very different implications for social solidarity than a spike in immigration, for instance. Plans to strengthen America’s social safety net — or, much more to the point, adopt a universal basic income — would buckle beneath a massive influx of immigrants. There are difficult questions around border security. There are very hard questions about how to integrate a lot of new people into American society (or any other society).

But the reason most often given is a bad one: the idea that more immigrants will take jobs from, and depress wages for, native-born workers. There’s overwhelming economic evidence that higher levels of immigration make most native-born workers better off. There’s mixed evidence on the effect on low-skill workers, but even if there are small losses, those are better managed through transfer programs than by closing the border.

When you’re thinking about competition between workers, the key question is how similar their skills are

This is where the analogy to birth rates is truly useful, though. When you’re thinking about competition between workers, the key question is how similar their skills are. Take two graduates from the same university, with the same grades, with the same major, with the same work experience, looking for the same kind of job, and an employer really might be able to play them off each other — and thus depress their wages. But take a law school graduate looking for a job with a firm and a high-school graduate looking for a job as an auto mechanic and they’re not going to compete with each other much at all.

Native-born workers compete with each other much more directly than they compete with immigrant workers. The single biggest reason is that native-born workers all speak fluent English, and the jobs you can get when you’re fluent in English are very different than the jobs you can get when you’re not. That means immigrants are less of a threat than new native-born Americans entering the work force. (An interesting wrinkle in this is that, by the same token, immigrants are more of a threat to each other. “The group that appears most vulnerable to competitive pressure from new low-skill migrants is recent low-skill migrants,” writes David Roodman in his survey of the economics of immigration.)

Which is all to say that if you’re worried about competition between workers then you should be more comfortable adding workers through immigration than through higher birth rates. But to my knowledge, almost no one actually is. It’s almost as if the core concern around immigration isn’t really wages for low-skill native-born workers at all.