THE Arizona law requiring police to check the immigration status of anyone they suspect of being in the country illegally — a statute tentatively blessed last week by the Supreme Court — is an invitation to abuse. It is all too likely to be used, as the court itself seemed to fear, to intimidate and demean people with the wrong accent or skin tone, thus delivering a get-out-the-humiliated-Hispanic-vote bonus to President Obama. The less likely alternative is that it will be applied more like the random T.S.A. searches at airports, thus infuriating Arizonans across the board.


While we wait for this to play out, let’s turn our attention to another aspect of the so-called “show me your papers” law: Show me WHAT papers? What documents are you supposed to have always on hand to convince police that you are legit?


Welcome to an American paradox. This country, unlike many other developed democracies, does not require a national identification card, because the same electorate that is so afraid America is being overrun by illegal aliens also fears that we are one short step away from becoming a police state.


I’ve suggested before that, as part of any comprehensive reform of our senseless immigration laws, Americans should master their anxieties about a national identification card. The Arizona controversy reinforces my conviction.


This is not a peripheral issue. The reason Arizona and other states have deputized police as amateur immigration agents — and contemplated making enforcers out of school principals, emergency-room nurses and other civil servants — is that we have failed so utterly to fortify the most obvious line of defense. No, not the Mexican border. Employers. Jobs are, after all, the main magnet for illegal immigration. If we had a reliable way for employers to check the legal status of prospective workers, and held them strictly accountable for doing so, we would not feel the need for all these secondary checkpoints.


What we have now is a laughably ineffective program called E-Verify, in which employers send information supplied by job applicants to be matched against databases in the Social Security Administration or the Department of Homeland Security. The most extensive study of this program, published in 2009, found it to be so easy to fool the system with stolen or fraudulent documents that more than half of the unauthorized job applicants got a green light.


In the absence of a credible federal system, frustrated states are improvising their own controls. For example, in many states you now have to prove U.S. citizenship or legal residency to get a driver’s license. This is presumably what most Arizonans will show police if they are challenged under the “show me” law. But by transforming a driver’s license into a kind of internal passport, Arizona and states with similar laws have created a different problem. Illegal immigrants don’t stop driving; they just drive unlicensed, untested and uninsured.


I understand that the idea of a national ID comes with some chilling history, which is why it has been opposed by activists on the right and left — by the libertarian Cato Institute and the A.C.L.U., by People for the American Way and the American Conservative Union. Opponents associate national identification cards with the Nazi roundups, the racial sorting of apartheid South Africa, the evils of the Soviet empire. Civil rights groups see in a national ID — especially one that might be required for admission to the voting booth — a shadow of the poll taxes and literacy tests used to deter black voters in the Jim Crow South. More recently, accounts of flawed watch-list databases and rampant identity theft feed fears for our privacy. The most potent argument against an ID is that the government — or some hacker — might access your information and use it to mess with your life.


“The one thing we know with certainty about databases is that they grow,” said Marc Rotenberg, executive director of the Electronic Privacy Information Center, which includes national ID cards on its list of threats. The official urge to amass and use information, he told me, “takes on a life of its own.”


But on the subject of privacy, we are an ambivalent nation. Americans — especially younger Americans, who swim in a sea of shared information — are casual to the point of recklessness about what we put online.


The trick, and I won’t pretend it’s always easy, is to distinguish the reasonable and constructive from the invasive and excessive. We want the sales clerk at the Gap to know our credit card is good, but not to have access to our whole credit history. We want our doctors to share our health histories with one another, but probably not with our employers. We may or may not want retailers to know what kind of books we read, what kind of car we drive, where we are thinking of traveling. We may or may not want those who follow us on the Web to know our real-time location, or our real name.