Today, a lot of Americans take the economic value of free trade as self-evident. That wasn't always the case.

By the same token, a lot of Americans today do not understand the economic value of labor mobility. Some day, that lack of understanding will seem arcane and ridiculous.

That's the opinion of Lant Pritchett, a former World Bank economist and Utah native. Pritchett is the subject of a lengthy interview in the latest issue of Reason, the magazine of the free-market, libertarian-minded Reason Foundation. The author of the new book, "Let their people come," he argues that migration is good for economies as well as for the poor people of the world.

His arguments make a lot of sense and ought to be read by everyone interested in the current debate over illegal immigration. Pritchett is no advocate of completely open borders, but he would like to "figure out ways of protecting the concerns people have about their country while at the same time allowing for more migration." It is possible, in other words, to allow people to work here without giving them all the benefits of citizenship. That sounds a lot like the guest-worker plan President Bush has presented.

Pritchett makes the case that the poverty is determined less by race, education level, gender or work ethic than by one all-important factor: "the country listed on your passport." And, while the world spends a lot of effort and money trying to solve global poverty, those efforts tend to be completely misguided.

He cites a World Bank report that said the 30 affluent nations in the Organization for Economic Cooperation and Development could help the poorest people in the world to the tune of $300 billion if they increased their labor forces by only 3 percent through liberalized immigration laws. By comparison, the developed world allocates only about $70 billion in foreign aid to the world's poorest countries today.

The difference goes deeper than that comparison, however. The $70 billion comes as a net loss to the rich countries. It simply floats away with no return. But a nation that expanded its immigrant work force by 3 percent would see a $51 billion gain through capital returns and production cost savings.

Pritchett compares the unwillingness to allow labor migration to apartheid.

"The idea of being American," he told the magazine, "is an idea of being open to people from other places coming and making a contribution. I think we've lost sight of that."

Like Pritchett, we hope the day comes soon when this economic principle becomes common wisdom.