In a week in which the European election results have shown the potency of the anti-immigrant vote in many countries, including Britain, Christopher Caldwell's contention that immigration has not only changed Europe but revolutionised it has a topical plausibility. Immigration, he says, and above all Muslim immigration, has planted in the heart of a weak and confused civilisation communities, rapidly growing in number, that have already changed Europe to suit their needs and beliefs. And the chances are, he insists, that in the future we will bend to their will rather than that they will bend to ours.

Rightwing rubbish? Caldwell cannot be so easily dismissed. True, he is a luminary of the Weekly Standard, the American neoconservative magazine Rupert Murdoch finances, but he is one of its more urbane and interesting voices. He knows Europe, especially France, better than most American and British commentators. His columns in the Financial Times frequently dispense a sharp common sense that many liberals find salutary, although not all might say so. He is very good at pinpointing denial and flight from reality, less good at offering convincing and practical alternatives.

Where he is right is in underlining the fact that immigration was encouraged by elites who took a ludicrously short-sighted view of its costs and consequences. The idea was to prop up industries already in decline and, later, to staff industries, such as health and tourism, the full cost of which our societies refused (and continue to refuse) to pay. The manning of underpaid and menial positions could be maintained only by a constant influx of new migrants, since people in established migrant communities either got better jobs or chose, like many in the native white population, to depend on the welfare state and to have no jobs at all. More recently, immigration has been defended as a way of making up for falling birth rates when, as Caldwell points out, it would have to be multiplied an unfeasibly large number of times to have that effect.

This inherently unstable and dysfunctional system was set in motion, in other words, for no good reason. Those who started it off did not foresee how big it would become, nor the mechanisms of family reunion and arranged marriages that would drive it on even when restrictions were belatedly imposed. Most of them did not imagine, says Caldwell, that the newcomers would "retain the habits and cultures of southern villages, clans, marketplaces, and mosques".

Either that, or they welcomed such retention. It was right and proper that the people Europe had lorded over should now come to the metropolitan countries: they would change us for the better. Not only were all cultures equal, but their cultures were more equal than ours. Caldwell quotes the philosopher Pierre-André Taguieff, who uses the term "immigrationisme" to describe the position that immigration is both inevitable and good. The truth is that immigration was not inevitable on the scale on which it took place, and that its effects have ranged from the pleasing - more ethnic food - to the positive - more cultural diversity - to the truly terrible - race riots, social tension, terrorist attacks.

Caldwell is good on the distorting effect of the universalist code that European politicians and intellectuals impose on discussion of immigration and the making of policy about it. Thus immigration is too often treated as one thing - as if New Zealand computer experts, American bankers and Polish plumbers fell into the same category as villagers from Pakistani Kashmir. Thus any trouble in immigrant communities must be understood in terms of alienation and exclusion, never in terms of aggression. Thus any restriction of rights must be cast within a general framework, so that, for instance, in order to ban headscarves from schools, the French government had to ban yarmulkes and "large crosses" as well, a transparent rigmarole.

When the Danish cartoons furore was at its height, newspapers the length and breadth of Europe upheld the right of free speech - yet the vast majority of them somehow neglected to reprint the offending sketches. The code insists, says Caldwell, that Islam must always be defined as a peaceful religion, yet ignores the way in which Muslim leaders in Europe lay down red lines that the non-Muslim majority is not supposed to cross. Once Muslim majorities emerge in certain towns and areas, Muslims will demand the right to live not only differently, but also separately, and Europe will lose control, Caldwell believes, of significant chunks of its territory. He ignores, in this worrying forecast, the diversity of Islam in Europe, and the often hidden ways in which Muslims in Europe are changing, as well as the strength of the secular European reaction if such developments threatened to become reality. One might reflect on the anxiety over black immigration a generation ago, and note how overdone it turned out to be.

It is not Islam's strength, however, that is at the core of Caldwell's analysis, but Europe's weakness. Like others of neoconservative bent, he has a Spenglerian sense that Europe has lost its sense of purpose. His book, one has to say, is not sure in the end of its own purpose. Is it a call for Europeans to look clear-sightedly at what immigration has wreaked and, in particular, to resist the overweening demands of some Muslims? Or is it a despairing commentary on the weakness of a Europe that has lost the capacity to do so?

But he is right to argue that immigration on the scale that Europe has experienced constitutes a risky experiment to which we need not have submitted ourselves, and of which the final result is not yet clear. He is right that we frequently talk about it in stupid and dishonest ways. If his book sharpens a so far sluggish debate, it will have served an important purpose.