For many economists, it's the simplest and most effective way to make the world richer and reduce poverty. For those in government, it's a political landmine.

Politicians on both sides of the Atlantic fervently oppose more immigration. In Europe, anti-immigrant parties are on the rise, fueled by the wave of refugees spilling out of the Middle East. In Britain, concerns over migration weighed heavily in the vote to leave the European Union.

In the United States, Donald Trump has made anti-immigration appeals a cornerstone of his candidacy, while Hillary Clinton has supported an overhaul of immigration laws that would allow people already in the U.S. to apply for citizenship while also enforcing border security. Last Friday, WikiLeaks released a leaked email purportedly showing that Clinton told Brazilian bankers in a private speech that she has a "dream" of a "hemispheric common market, with open trade and open borders," sparking criticism from Republicans. Clinton's campaign manager responded in a televised interview that the candidate "absolutely" opposes "throwing open our borders."

From the perspective of many economists, however, it's a shame more politicians don't support giving people the greater freedom to move across national borders. Some economists have suggested that allowing people to work where their labor is most highly valued — something that is hardly realistic, given the political environment in the developed world— could double the size of the global economy. More than a dozen studies reviewed by economist Michael Clemens, a senior fellow at the pro-immigration Center for Global Development, suggested that eliminating barriers to global mobility would increase world gross domestic product by between 67 and 147 percent.

Clemens says the benefits are huge even for a more modest loosening of restrictions on immigration. His research suggests that allowing just 5 percent of the people now living in poor countries to work temporarily or permanently in richer countries would add trillions of dollars to the global economy. The economic gains would be greater than those from dismantling every remaining barrier to trade and investment around the world.

Not all economists agree with these arguments. Harvard economist George Borjas, for example, has made the case that more immigration into developed countries would produce large gains for some groups, such as wealthy executives and investors, but that native workers would lose out. "In the end, immigration will almost certainly improve the economic well-being of some Americans, but other Americans will be worse off," he has written.

Others argue that there are strong non-economic reasons to oppose additional immigration, such as concerns over national security or national identity.

What's the case for benefits?

The argument is essentially two-fold.

First, the same worker can create more economic value in some places than in others, because of differences in factors that affect the productivity of businesses, such as natural resources, infrastructure, technologies and laws. For example, a worker skilled in math is more likely to excel in a country with computers, while a natural entrepreneur will thrive in a region where laws make it easy to start businesses.

Differences in productivity are reflected in the vastly different wages people can earn for similar types of work across the world. According to estimates by Clemens, Claudio Montenegro and Lant Pritchett, who examined a data set of more than 2 million workers, the average Peruvian can make 2.6 times as much in the United States as in Peru, while a Haitian can make seven times more.

"Right now, you have a ton of human talent, billions of people, stuck in countries where it’s hard to get anything done," says Bryan Caplan, a professor of economics at George Mason University. "Think about what you could accomplish in Haiti. Not very much -- it’s a messed-up place. There are so many people trapped in these places."

Second, many economists say that an influx of immigrants can expand an economy, potentially even raising wages for the native born.

While economic studies have produced varying results, most have shown that immigrants have a neutral or positive impact on the job prospects of native-born Americans. An expansive study released by the National Academies of Sciences in September found that immigration has mostly helped the U.S. economy in recent decades and had little effect on the wages or employment of native-born Americans.

According to the study, the main group negatively affected by newly arriving immigrants was actually earlier waves of immigrants with similar language skills. To a lesser extent, new immigrants also competed for work with the lowest-skilled Americans, such as high-school dropouts. But in general, immigration left the native population slightly better off.

Angel Gurría, the secretary-general of the Organization for Economic Co-operation and Development, said in a recent interview in Washington that the effects of migration are net positive, even fiscally. "How is it possible? Well, take a country like Spain. They were growing fast, there was a lot of construction, and they imported 5 million immigrants from Latin America," he said. Millions of immigrants came into the country legally and paid taxes under bilateral agreements.

"They actually financially saved the social security system, or at least deferred for five or 10 years the time of reckoning. Because young people pay taxes, but they don’t get sick, and they don’t use retirement funds," he said.

Borjas, the Harvard professor, has argued, however, that unrestricted immigration can place a fiscal burden on a state, and that the gains from immigration depend largely on whether receiving countries build enough infrastructure to accommodate them. Immigrants aren't just perfect cogs in the machine of the economy, he says -- they are real people, and their presence raises real questions about how they and their descendants fit into a society.

Polls of economists' views reflect this debate. In a survey of more than 40 of the nation's most prominent economists, half agreed that the average U.S. citizen would be better off if a large number of low-skilled foreign workers were legally allowed to enter the United States each year. Twenty-eight percent said they were uncertain, and 9 percent disagreed.

However, they also recognized the costs of such policies. Nearly half of the economists also agreed that, unless they were compensated by others, many low-skilled Americans would be worse off.

A moral case

Beyond economics, some argue there's a moral case for allowing more immigration.

"Immigration restrictions are government-required discrimination against people who have done nothing more than be born in another country," Caplan says.

Alex Tabarrok of George Mason University, a colleague of Caplan's, has also made the case for looser border restrictions, arguing that freedom of movement and access to opportunity are basic human rights. Limits on immigration defy every standard moral framework, he says, and eliminating them would result in an increase in global human freedom comparable to the abolition of slavery and the recognition of the rights of women.

“Closed borders are one of the world’s greatest moral failings,” he writes.

Not all economists see things in such an unbridled way.

For example, Larry Summers, a former Treasury secretary who's in the mainstream of Democratic economic thinking, has said that what the world needs is "responsible nationalism."

"A new approach has to begin from the idea that the basic responsibility of government is to maximize the welfare of citizens, not to pursue some abstract concept of the global good," he wrote in an opinion piece for The Post.

While Clemens says he is troubled by the idea of discriminating against people based on where they are born, he doesn't advocate “open borders," a term that is often used as a synonym for anarchy -- no background checks, no deportation and no restrictions on immigration. In reality, few politicians are advocating even moderately higher levels of immigration, and the world won't see anything like open borders anytime soon. But he says people still should recognize the substantial trade-offs of the current system.

Clemens draws an analogy with the rights of women. In the United States, laws prevented women from owning property, inheriting wealth and entering many professions until the late 1800s. Although some male workers may have suffered from the entry of women into the workforce during the 20th century, no one would deny that it has provided enormous benefits to the country and the economy. Yet restrictions on women had still persisted for millennia.

“The ability of societies to create and maintain institutions that have vast economic and social costs is not in doubt," he said.

You might also like: