Will anyone speak up for Arizona and its new immigration law?

The state abused by Jon Stewart as the “meth lab” of democracy has been forced to deal alone with a problem created and then ignored by the national government. Arizona’s answer is not perfect, but it is not unreasonable either—and should jerk the national conscience to attention.

Imagine yourself a landowner in southern Arizona. The border between San Diego and Tijuana is now effectively fenced, so the flow of illegal immigration has been diverted to your front yard. Every morning you wake up to a hillock of garbage: plastic bottles, food remains, human urine and feces. If you try to police your land, you put your life at risk: Last month, Arizona rancher Rob Krentz was murdered on his own property, likely by a marijuana-smuggling illegal migrant.

Mexico’s drug war has reached into Arizona cities. Federal authorities capture an average of 1.5 tons of marijuana per day in Arizona. Drug-related kidnappings, tortures, and murders of illegals by illegals have made Phoenix one of the most violent cities in the United States. Illegals crowd hospital emergency rooms, crash uninsured cars, and transform overbuilt neighborhoods into rooming house slums. Their children have the right, under a 1982 Supreme Court decision, to attend local schools at local expense, crowding the classrooms of native-born children, whose educations are further undermined when substantial numbers of their classmates cannot speak English.

Yet not only does the law go unenforced, not only has work not even started on the immigration fence that Congress supposedly voted to build two years ago, but the authorities in Washington keep talking up a proposed amnesty (sorry: “pathway to citizenship”) that only invites more illegals to rush into the U.S. to take advantage of this dazzling opportunity. And when people complain, when a state legislature like Arizona’s takes what action it can against a crisis incubated over 20 years by an unspoken federal policy to look the other way—they are vilified as haters and racists.

The most effective section of the new Arizona law grants local police the same powers to deal with illegal migrants that New York City used in the 1990s to deal with illegal guns. Police cannot stop people on mere suspicion. They cannot stop them for being brown. But IF police have stopped someone for an offense or infraction—drunk driving, for example—they can then ask for proof of legal residency, just as New York City police will search a car for illegal weapons.

In the past, such a request by Arizona police would have been a waste of time, since police lacked the power to act even if they had apprehended an illegal migrant. Now that illegal immigration has been made an offense under state law (in addition to federal law), police can detain an illegal. Obviously Arizona does not have facilities to detain the estimated 600,000 or more illegals in the state. But it can at least get the drunk drivers off the streets (a large and deadly problem in the state). It can hold for deportation those with a history of involvement in the drug trade without having to initiate further lengthy legal procedures. And it can prod a reluctant federal immigration service into action.

The true benefit of Arizona’s new law however is not deportation, but deterrence.

Amnesty proponents often argue that it would be impossible to round up and expel the estimated 12 million illegals in the U.S. They are right, of course.

But it would be very possible to enforce immigration law in such a way that illegal immigration becomes a less attractive proposition, by discouraging illegal entry and encouraging those who are here illegally to return home of their own accord.

New York City did not reduce gun violence in the 1990s by arresting everyone who violated a gun possession law. It took relatively few arrests to persuade potential lawbreakers to alter their behavior and leave their guns at home.

The experience of the past two years has shown that migration responds swiftly to changing incentives. The Center for Immigration Studies has tracked monthly census data for young Hispanic males with low levels of education—a good proxy for the illegal immigrant population. Between the summer of 2007 and the first quarter of 2009, that population actually declined. Extrapolating from survey figures, CIS estimates that the illegal population in the U.S. dropped by 1.7 million during the recession. The number of illegals entering the country fell by about one-third while the number returning home doubled .

States and counties that have strengthened enforcement have seen declines in the population of non-English-speaking students in local schools (another good proxy for the illegal immigrant population).

Arizona’s law seeks a similar effect. It’s no substitute for federal enforcement. But it’s a big improvement over all the loose talk of amnesty. If you find the measure excessive, don’t blame the state. Blame those in Washington who made state action necessary—as the only alternative to federal inaction.