The United States has long been known as a country of immigrants. Yet more than two hundred years after the nation’s founding, policymakers cannot agree on whether America should continue to accept foreign-born citizens. Some are particularly concerned about the recent wave of Hispanic and Asian immigrants and the relatively high birthrates among these groups. The U.S. Census Bureau predicts that by the year 2050, the Latino population will increase from 10 percent to 25 percent, while the Asian population will increase from 3 percent to 8 percent. Although the black American population will remain relatively stable at 14 percent, the percentage of native-born whites will decrease from 74 percent to 53 percent. By 2010, several states will no longer have a “majority” ethnic group—that is, a group that comprises more than 50 percent of the population.

Some analysts fear that such dramatic changes in America...