In 1994, Californians voted in favor of Proposition 187, which barred illegal immigrants from receiving publicly funded education, social services and health care. The proposition also required that local law enforcement authorities, school administrators, social and health care workers report anyone they suspected of being in the country illegally.

Proposition 187 immediately became a divisive political issue. The law’s most visible proponent, California governor Pete Wilson, got re-elected due in least in part to his stance on Proposition 187. Students in California’s colleges protested the proposition, calling it mean-spirited and unfair. Health workers and educators protested the new role thrust upon them as informants. Indeed, the proposition highlighted the deep divide that separates those who believe that illegal immigration harms the United States and those who believe it does not.

The argument made by the supporters of Proposition 187 was based...