Both liberals and free-market libertarians often see [the illegal immigration debate] as an abstract issue about poor people being hindered from moving to jobs by an arbitrary border drawn across the southwest desert.

Intellectuals' ability to think of people in the abstract is a dangerous talent in a world where people differ in all the ways that make them people. The cultures and surrounding circumstances of those people are crucial for understanding what they are likely to do and what the consequences are likely to be.

Some free-market advocates argue that the same principle which justifies free international trade in commodities should justify the free movement of people as well. But this ignores the fact that people have consequences that go far beyond the consequences of commodities.

Commodities are used up and vanish. People generate more people, who become a permanent and expanding part of the country's population and electorate.

It is an irreversible process -- and a potentially dangerous process, as Europeans have discovered with their "guest worker" programs that have brought in many Muslims who are fundamentally hostile to the culture and the people that welcomed them.

Unlike commodities, people in a welfare state have legal claims on other people's tax dollars and expensive services in schools and hospitals, not to mention the high cost of imprisoning many of them who commit crimes.

Immigrants in past centuries came here to become Americans, not to remain foreigners, much less to proclaim the rights of their homelands to reclaim American soil, as some of the Mexican activist groups have done.