The problem with Arizona’s new statute to “discourage and deter the unlawful entry and presence of aliens” is not its stated purpose but why and how it seeks to achieve that purpose.

Our borders, particularly with Mexico, are porous. It’s estimated that as many as 500,000 undocumented aliens enter the U.S. annually, overwhelming 20,000 federal Border Patrol agents charged with protecting the 1,900-mile boundary with our southern neighbor, not to mention 5,000 miles of border with Canada and 12,000 miles of coastline.

Arizona’s new law, in effect, deputizes the state’s officials as nonfederal agents to detect, apprehend and deliver into federal custody undocumented aliens found on its soil.

So what’s wrong with that?

Well, for one thing, Arizona’s law has been criticized as infringing the civil rights of people of color – by permitting police and other state and local officials to check the immigration status of any person, where there’s “reasonable suspicion” to believe that person is an illegal alien. Critics suspect, rightly so, that “reasonable suspicion” will be triggered by any dark complexion or foreign accent. Don’t expect too many white stock brokers or soccer moms to be subjected to a document check.

For another, it’s probably unconstitutional. The Constitution gives Congress the exclusive right to create a “uniform Rule of Naturalization.” The Immigration and Nationality Act, first passed in 1952, authorizes state enforcement of certain of its criminal provisions, but not its civil measures for detention and removal of noncitizens. Under the “pre-emption” doctrine, federal law will likely trump any state law on immigration enforcement, thereby favoring uniformity of immigration policy across the country.

Most importantly, there’s the nasty attitude of Arizona Gov. Jan Brewer and those legislators who enacted the law – a desire to pander to voters with a xenophobic outlook, characterized by the belief that immigration is bad and aliens, legal or illegal, should stay home.

We are, it is often said, a nation of immigrants, but the arrival of each new immigration wave over the past 160 years has stirred dark societal emotions, ranging from suspicion to resentment to outright hysteria.

Such anti-immigrant feelings tend to intensify during times of war, economic distress or social upheaval. The current stagnant economy, with its high unemployment and home foreclosure rates, has become a hothouse for such hatred.

Just think of our local experience in Lewiston — the anger generated by several thousand Somali refugees settling here over the past decade, and, before that, Irish immigrants arriving in the 1840s and 1850s and French-Canadians starting in the 1860s.

During the 19th and early 20th centuries, nationwide “nativist” movements — like the Know Nothings, American Protective Association, Immigration Restriction League, and Ku Klux Klan — pressed to limit entry of Irish Catholics, Chinese, Japanese, and Southern and Eastern Europeans into the U.S. on overtly racist grounds.

Today many Americans believe the U.S. is being overrun by illegal immigrants, who are stealing jobs, inundating welfare rolls, ruining schools, and bringing violence and drugs into the streets. Those beliefs seem particularly strong in regions lying directly astride the path of the heaviest Hispanic influx, like Arizona.

To such folks, Arizona’s law represents a necessary response to what they see as Washington’s abdication of its duty to repulse an invasion. They want a high wall or fence along the southern border to keep out illegals as well as mass deportation of undocumented aliens already here.

While it’s true that a country’s ability to control its borders and regulate immigration is both a significant aspect of sovereignty and a desirable mechanism to protect security and promote economic and social stability, it’s also important to recognize the valuable role immigrants play in our society. They have allowed this country to continually re-invent itself and stay vigorous.

Many of our greatest inventors and scientists, for instance, have been immigrants. A short list would include Nikola Tesla, who pioneered commercial electrical power generation, European refugees who developed the A-bomb, and German rocket specialists who helped create the American space program. As late as 2009, four out of seven U.S. Nobel prize winners were born outside this country.

Not just science, but our cuisine, architecture, music, language and literature, have benefited from the eclectic influences brought here by immigrants.

At a more basic level, it is immigrants who typically accept menial, grueling and sometimes dangerous positions as migrant farm laborers, kitchen help, poultry workers, janitors and domestic servants, jobs usually snubbed by native-born citizens.

So, by all means, let’s find a way to reform immigration laws and get illegal immigration under control, but let’s try to do it rationally and humanely. That will require a serious, thoughtful debate about a whole spectrum of alternative solutions, not a shouting match.

Who should we let in and in what numbers? Should the primary criteria for admission be skills and brains or calloused hands? Should we emphasize national economic needs, unification of families, regional diversity, humanitarian relief, refuge from persecution, capacity to become self-supporting, or some combination of the above?

What about enforcement? Should we require a national identity card? Institute random document checks at mass transit stations, car rental agencies, auto license/ registration centers, schools and other public places? Should we impose stiff jail sentences on employers who hire undocumented aliens? Expedite deportation procedures?

There are no simple answers to these questions. They are susceptible to resolution, but only if the volume of angry rhetoric is turned down.

It has taken many compromises to create our “melting pot” society of immigrants, and it will take many more to sustain it.