Multiculturalism has become a fraught issue throughout Europe in recent years. A rancorous chorus of populist politicians, like Geert Wilders in the Netherlands and Jimmie Akesson in Sweden, have made major electoral gains by stoking fears about multiculturalism. Mainstream politicians have joined in, too. Prime Minister David Cameron of Britain and Chancellor Angela Merkel of Germany have recently made deeply critical speeches, and the Dutch government decided last month to dump a decades-old policy of multiculturalism.

The real target of much of this criticism, however, is not multiculturalism but immigration and immigrants — especially Muslims. Mr. Wilders, leader of the Freedom Party, the third largest in the Dutch Parliament, has campaigned for an end to all non-Western immigration, a ban on mosque building and the outlawing of the Koran. Mr. Akesson, whose far-right Sweden Democrats shocked the nation by winning 20 seats in last year’s parliamentary elections, denounces immigration as the biggest threat facing Sweden since World War II. Centrists have responded not by challenging such prejudice but by appropriating the right’s arguments in an effort to hold on to votes.

Part of the difficulty in thinking about multiculturalism is that it has come to have two meanings that are rarely distinguished. On one hand, it refers to a society made diverse by mass immigration, and on the other to the policies governments employ to manage such diversity. The failure to distinguish between these meanings has made it easier to use attacks on multiculturalism as a means of blaming minorities for the failure of government policy.

Mass immigration has been a boon to Western Europe. It has brought great economic benefits and helped create societies that are less insular, more vibrant and more cosmopolitan. But the policies designed to manage immigration have been largely a disaster. To see why, one needs only to look at the experience of Britain and Germany. Both have adopted multicultural policies, though they have taken different paths. The consequences, however, have been similar.

Thirty years ago, Britain was a very different place than it is now. Racism was vicious, visceral and often fatal. “Paki bashing,” the pastime of hunting down and beating up Britons with brown skin, became a national sport in certain circles. I remember organizing patrols on the streets of East London during the 1980s to protect South Asian families from rampaging racist thugs. Workplace discrimination was endemic and police brutality frighteningly common. Anger at such treatment came to an explosive climax in the riots that rocked London, Liverpool, Birmingham, Bristol and other cities during the late 1970s and early 1980s. It was in response to this rage that Britain’s multicultural policies emerged.