Jonathan Wajskol, an Italian graphic designer who moved to the United States about three decades ago, has a life with the hallmarks of an immigrant success story: graduate studies at an American university; a successful international business with partners in Milan and Beijing; and a residence in Greenwich Village that he shares with his wife and two children.

One thing he does not have, however, is American citizenship — and that is a deliberate choice. He has a green card, but he has never applied for citizenship and is not interested. His reasons, he said, go to the heart of his identity.

“I would feel that if I get the American citizenship, I would feel a little less Italian,” he explained. “I really don’t feel American.”

For many people around the world, a U.S. passport is a near-sacred goal, and given half a chance to get one, they would hungrily seize it. In Washington, the partisan debate over immigration has become mired, in part, over whether to provide a path to citizenship for the estimated 11 million undocumented immigrants in the United States.

But even as legions here and abroad pin their hopes on becoming American, and the country wrestles with emotionally-fraught questions over who should have that right, there is a seemingly contradictory truth: that millions of people who are in the country legally, and stand on the threshold of citizenship, never take that next step.

According to some estimates, about 40 percent of all people who hold green cards, the gateway to citizenship, do not naturalize.

Of those, many may want to apply but are deterred by a variety of reasons, including the $680 application fee or the requirement that most applicants must prove they can read, write and speak basic English, immigrants’ advocates said. Some countries — including Japan, China and Iran — generally do not permit their citizens to acquire a second nationality, forcing a difficult choice.

But alongside those potential applicants, there is a vast population of green card holders who have everything they need to naturalize, including the language skills, money, sufficient time of residence in the United States, permission from their native countries and a clean criminal record. All they lack is the desire.

They simply don’t want it — or want it enough — and cite various reasons, including an overriding patriotism for their native country, disaffection for the policies of the U.S. government, even simple fecklessness.

“So often in textbooks about immigration, the cover illustration is the naturalization ceremony with the American flag and a group of immigrants, highly diverse by race,” said Alan Hyde, a Rutgers University professor who teaches immigration law and was a co-author of a recent study about why some people do not naturalize. “So much that is written on immigration just assumes that they come, they assimilate, they get green cards and they naturalize.”

But, he added, a different reality exists for so many other immigrants — those who don’t want to naturalize. “Most people don’t know it’s a distinctive feature of America,” Hyde said.

For Wajskol, whose wife and children are U.S. citizens, the question of naturalization bubbled up from time to time. He even filled out the paperwork, he said. But he never followed through.

“I don’t have an Italian name, so as it is, I have a slight identity crisis,” he said. “Being American would taint my Italianness a little bit more.”

If he has one misgiving about his position, he said, it would be that he cannot fully participate in the American electoral process. Only citizens have the right to vote in federal elections and in most local elections.

But aside from that, Wajskol said: “I really have everything that I need. I am treated pretty much just like a citizen.”

Lawful permanent residents are eligible to apply for naturalization after meeting certain requirements, including a minimum length of residency, which for most candidates is five years.

In the meantime, they have many of the same rights and obligations as citizens, including permission to work. They are also bound by largely the same tax rules.

But in addition to limited or no voting rights, lawful permanent residents cannot make their home in a foreign country or remain outside the United States for extended periods of time, except in specific circumstances. They are ineligible, in many cases, for Civil Service jobs and certain government assistance. And they can be deported for violating any of a wide variety of laws.

Still, none of these disadvantages has been enough to compel many lawful permanent residents to stand and take the oath of allegiance.

Xiaoning Wang, who was born in Beijing and moved to New York City in 1994, owns ChinaSprout, a company that distributes Chinese cultural and educational products. She has a green card yet no urge to naturalize.

“I love New York, I love the United States, I love everything here and the opportunity that I have in this country,” said Wang, who is married to a German and has German nationality. “I just don’t see the advantage” of being naturalized, she added.

Alain De Beaufort, a Colombian with a green card, moved to the United States six years ago and married an American; they now have two U.S.-born children and live in Brooklyn.

For a while, he said, laziness thwarted any vague interest in naturalizing. But his ennui has given way to a more profound reason: a growing disillusionment with the United States, particularly its foreign policy.

When he was growing up in Latin America, the United States and the idea of American citizenship were very attractive, he said. But in recent years, he said, he has opposed aspects of U.S. foreign policy, including practices at the Guantanamo detention center and the expanded use of drones for targeted strikes. As a result, his view has shifted.

“It’s not as glamorous to be a U.S. citizen anymore,” said De Beaufort, a writer and restaurant server.

But De Beaufort allowed that the conveniences of citizenship might eventually trump his idealism. Indeed, while the people who naturalized in 2012 spent a median of seven years with a green card before naturalizing, according to the federal government, some waited much longer.