TUCSON, Arizona — It is eerie and ugly, coming home to a state of the union that now incites cops to roust fourth-generation Americans on the simple evidence of a suntan. That smacks of what evil empires do.

Arizona is not yet Azerbaijan but neither is it, any longer, the big-hearted Mexican-accented place I loved to say I was from. “Oh right,” a friend remarked the other day in New York, “the hate state.”

A new guilty-until-proven-innocent law allows police to detain anyone on the mere suspicion of having sneaked across the Mexican border.

The irony rankles. Many Mexican-Americans who now must fear any law officer in a bad mood have family roots far deeper than Arizona’s 1912 statehood. Most people who want them gone are relative newcomers.

True enough, illegal immigration from Mexico is a problem, and so is drug trafficking. But building barriers, physical or psychic, only brings on worse crises and undermines what America represents.

For an Arizonan-at-heart like me, this is personal. My father ended up here from a different direction, welcomed at Ellis Island by that towering statue that is supposed to define us.

Arizona’s new law led the news on Al Jazeera. It is the butt of bitter jokes across Europe. People are losing their last shreds of faith in the nation that once symbolized liberty and tolerance.

Who can blame them? Ronald Reagan earned his place in history by thundering: “Mr. Gorbachev, tear down that wall.” Now his spiritual heirs want to put it back up in Arizona.

Gov. Jan Brewer assures that this is not about racial profiling. Everyone, dark or light, needs identity papers to produce for no particular reason. Remember those old Nazi films? “Vos papiers!”

Nations must patrol their borders and enforce their laws. But when they target broad ethnic groups, or generalized categories, they venture dangerously close to what we have fought wars to thwart.

This closing of the Arizonan mind comes simultaneously with ecological peril: the squandering of scarce water and the relentless bulldozing of the dramatic Sonora desert landscape found nowhere else.

In Massachusetts, I visited Alan Weisman, whose best-selling “The World Without Us” looks hard at such things. Fed up with Arizona’s changing face, a while back, he sold his Tucson house and burrowed into the Berkshires.

When people are fearful, Weisman says, they tend towards easy — and invariably wrong — measures. They give authorities license to attack obvious surface symptoms while the underlying causes fester.

The recent murder of a rancher on the border sparked exactly this response: buy more guns, round up the usual suspects and slam the door. But that only swells the ranks of desperados with nothing to lose.

We would do better to understand the problems we are trying to solve. For starters, we ought to consider the human realities. Broad stereotypes are as unhelpful as they are ignorant.

“Mexicans,” no one should be surprised to learn, include a whole lot of hard-working, law-abiding folks with family values who hate drugs and crime. Some, fabulously rich, could put gringos to work. Plenty of others can enrich America’s intellectual capital.

But if some are drawn north by choice, illegal immigration is far more of a push than a pull.

In part because of U.S. policies, Mexico has lost much of its arable land. Young people, less rooted in old traditions, want a better life than near slavery in a border manufacturing plant.

For many, those harrowing trips across the border are acts of desperation to feed hungry families. Sensibly designed aid programs would allow them to stay home, earn incomes and buy American exports.

Drug trafficking is a separate issue, and hapless Mexicans along the border suffer from it more than Americans. Decriminalizing the small stuff would free lawmen to go after gang leaders at the top.

As policy debates rage on, we might stop to reflect on what is at risk. As anyone with Arizona bloodlines can tell you, it is a lot.

I only got here when I was 3. My father, who escaped Bolshevik Russia and went to Wisconsin, discovered Tucson in 1946. He ran El Tampico Bar in the heart of the old town, a cluster of Mexican barrios.

Arizona was sun-baked and laid back, a land of gorgeous gorges, Indian lore and green corn tamales. In Tucson, the people who wore guns could mostly shoot straight.

In the 1970s, developers tore down the mud wall and the Spanish-style plaza of the oldest continually settled city in North America. Water wasters dried up the Santa Cruz River, killing the cottonwoods.

By then I was living in Paris, in awe at how careful planning could add in so much of modern times and so many different cultures yet still preserve the soul of a 2,000-year-old city.

Until only recently, French friends sought my advice on travel to Arizona. For them, “Weet Ehrp,” the legendary Tombstone marshal, ranked up there with Asterix le Gaulois as a folklore hero.

These days, the Arizona lawman they picture is a swaggering bully in Maricopa County, a sheriff who crows that the new immigration law will allow him freedom to get serious. And not many plan to visit.