If you enforce it, they will leave

Tougher laws that penalize businesses that hire illegals and a slowing economy are responsible for many illegals heading back to Mexico.
In Arizona:
“A federal judge on Thursday upheld an Arizona law that prohibits businesses from knowingly hiring illegal immigrants and yanks the business licenses of those that do. U.S. District Judge Neil Wake dismissed a lawsuit filed by business groups that argued that federal immigration law severely restricts Arizona's ability to punish people who knowingly employ illegal immigrants.”

State Representative Russell K. Pearce, a Republican from Mesa and leading advocate of the crackdown on illegal immigration, takes reports of unauthorized workers leaving as a sign of success. An estimated one in 10 workers in Arizona are Hispanic immigrants, both legal and illegal, twice the national average.

“The desired effect was, we don’t have the red carpet out for illegal aliens,” Mr. Pearce said, adding that while “most of these are good people” they are a “tremendous burden” on public services.

Elizabeth Leon, a legal immigrant and day care worker, said the families of two of her charges abruptly left, forcing the state to take custody of the children.
I'm sorry but does this make sense to you? Leave your kids behind.

Even the legal immigrants have come to realize that they are being hurt by the illegal invasion.
"Juan Leon, a construction subcontractor and the husband of Elizabeth Leon, the day care worker, said illegal immigrants had made it harder for legal residents like him to find work. Companies that employ them can bid much lower on projects than he can because they pay workers much less, Mr. Leon said.

“I hate to see families torn apart,” he said of the current flight, “but there is no money to be made sometimes because some contractors who employ illegal workers can do the job dirt cheap.”