In this climate of unease, a fierce debate has surfaced in Britain and drawn attention across Europe. It emerged not from the political right, where most immigration issues erupt, but from the left, where European progressives are pondering a troubling new dilemma: will mass immigration be the undoing of Europe’s cherished welfare state?

The argument goes like this: immigration brings diversity, which erodes the sense of shared values and solidarity that has kept enlightened European socialism alive in a world of free markets and rampant capitalism. Those debating the point talk of models. They look at Sweden and see a fairly homogenous society of taxpayers happy to fork over 60 percent of their income in exchange for generous social benefits. They look at America and see a wildly diverse society whose taxes–under 30 percent, on average–provide for only the flimsiest of safety nets. No national health insurance, no long-term unemployment benefits, no security of the sort that Western Europeans take for granted. As immigration, legal and illegal, begins to transform much of Europe into a melting pot, they realize they may soon face a set of seemingly impossible choices. Will their Europe of the future remain like Sweden, or become more like America? And is there a trade-off between solidarity and diversity, such that Europe’s social-welfare states can survive?

The choice may not be quite that stark. But clearly, immigration will reshape Europe. Its population is aging rapidly, dragging down economic growth and putting tremendous pressure on underfunded pensions. According to the American demographer Bill Frey, the median age in the EU by 2050 will be 52.7 years, compared with 36.2 years in the United States.

Enlargement will do little to ease Europe’s demographic bind. Birth rates in Estonia, Lithuania and the Czech Republic are among the lowest in the world. Immigration from outside the new 25-member EU will therefore become essential to Europe’s economic well-being. But that very fact will force adjustments. Europe’s sizable non-Christian minority is already the fastest-growing segment of the continental population, and in some countries that has become a source of deep anxiety. The Netherlands, by some estimates, will have a school-age Muslim majority by 2050.

Such trends cannot help but have a major impact on social policy. Unlike the United States, where large-scale (but relatively well-managed) immigration has helped boost American productivity and entrepreneurship, Europe has largely discouraged economic immigration. The result: migrants from around the world found the only way to live and work in Europe was, in effect, to break in and claim asylum. “You’re left with a situation in which every immigrant begins to look problematic,” says Charles Westin of Stockholm University. Ferruccio Pastore of the Center for the Study of International Politics in Rome says the system suffers from “chronic immigration schizophrenia.”

One consequence has been to rob Europe of much of the beneficial effects of foreign labor. Through the early 1990s, Germany had no comprehensive immigration policy. It did have one of the world’s most liberal asylum laws, and attracted more than 1 million refugees during just a few years. The laws have since changed and the numbers declined, but immigrants remain disproportionately dependent on state assistance: 8.3 percent of immigrants are on welfare, compared with 3.3 percent of native Germans. Similarly, joblessness among immigrants (21.2 percent) is more than twice that of the German-born population. “For 50 years,” says Stephanie Wahl of the Institute for Economics and Society in Bonn, “we’ve taken in poorly skilled immigrants without thinking much about what would happen.”

The picture was much the same across the rest of Europe. And politicians reacted in much the same way. Rather than tackle difficult underlying economic issues, they went after “asylum seekers”–Europe’s catchall phrase for virtually all immigrants–urged on by baying tabloids and insecure citizenries. From Dublin to Berlin, governments cracked down. Germany began turning away refugees. It sped up deportation procedures and cut welfare payments. Asylum applications are now down to about 50,000 a year.

This climate of fear still rules. In advance of the May 1 enlargement, alarmed by the prospect of invading East European job seekers, Denmark’s conservative government passed a law granting benefits to immigrants only after they’ve been in the country for seven years. Germany’s socialists, along with most other EU governments, adopted similar measures. The barriers take different forms, from residency tests and waiting periods to outright prohibitions. But these are little more than stopgaps. With time, more-enlightened measures will surely be adopted. Britain, France, Germany and Spain, in fact, are moving toward U.S.-style policies. By managing and controlling immigration, they hope to reap the economic benefits of immigration while muting public unease.

But will it work? This is the unsettling question posed recently by David Goodhart, a respected voice of the British left who started thinking about immigration and its effect on the traditional welfare state that sits at the core of Europe’s identity. In a 6,200-word article titled “Too Diverse?” in the February issue of Prospect, the current-affairs magazine he edits, Goodhart sparked a great row by suggesting that diversity and social welfare don’t mix. His thesis: Europe’s welfare state thrives on homogeneity. People who are alike find it easier to give up something (e.g., taxes) to take care of one another. Diversity, he argues, might undermine this social compact, as it has in America. “To put it bluntly,” he wrote, “most of us prefer our own kind.” We share our wealth when “people like us” fall into hardship and need help; we are wary of immigrants or others who might not share those values, partly for fear that they will exploit the system and our generosity.

Goodhart, though deliberately provocative, still did not foresee the firestorm that greeted his article–especially after it was reprinted in the Guardian newspaper for a wider audience. In response, A. Sivanandan of the Institute of Race Relations likened the essay to Thatcherite Little Englandism dressed up “in liberal rhetoric and pseudo-intellectualism.” The Guardian’s Gary Younge wrote: “There is indeed a progressive dilemma. It’s the dilemma of what to do with people who pose as progressives and preach like reactionaries.”

For a change, however, the debate over immigration was liberated from London’s tabloids and entered the intellectual and political mainstream. Whether Goodhart is right or not is almost moot. “All the survey evidence indicates that as society becomes more diverse, support for public spending on core state services increases,” writes Peter Taylor-Gooby of the University of Kent. Or maybe not, suggests Peter Lindert, author of “Social Spending and Economic Growth Since the 18th Century.” Immigration, he says, “lowers society’s willingness to tax and spend on social services”–but it shouldn’t, he says. “The political tensions are based on a false premise.” The fact is, Europe’s future is a huge and irreversible social experiment. Europe needs to get it right.