Why are some in the West so terrified of Muslims? There are many tediously familiar answers: because they are all potential terrorists, because they are a drain on the social services, because their culture threatens to swamp British civilisation and so on.
There is, however, a more subtle reason for Islamophobia. Think of the sheer strangeness, in the eyes of sceptical modern Europe, of the presence of countless millions of ordinary men and women whose everyday lives are shaped and guided by belief. What sense can an agnostic, pragmatic society make of that? How can faith possibly fit into its materialistic priorities?
In the European world bus drivers, florists and dental assistants are not usually expected to hold complex ideas about the origins of the world, the purpose of life, or what it means to live a rich, fulfilled, fully human existence. They are simply expected to get on with their everyday lives and leave these more fundamental questions to scholars and clerics. This is not so in the case of Islam. A Muslim bank clerk or taxi driver is expected to be as concerned about these questions as an imam.
Antonio Gramsci maintained that all ordinary people were at a certain level philosophers, but this is a lot more obvious in the Islamic world than it is elsewhere. Islamists are also natural-born internationalists.
The faith they share is not one confined to national cultures. It links them to a global community of believers and overrides all narrowly parochial concerns.
Western societies deal with belief primarily by reducing it to a private affair. It becomes a kind of hobby or personal eccentricity, rather like collecting Javanese parrots or engaging in sado-masochistic pursuits. It is not even something that happens between consenting adults, but is as much one's own affair as flossing your teeth. It thus has no collective or political dimension at all. It is not a force for the transformation of reality but a refuge from it, like Madonna's Kabbalah or Tom Cruise's Scientology. Belief is what you do in your spare time. As the old joke has it, the moment it starts to interfere with your everyday life, it's time to give it up.
Islam, by contrast, makes no such absolute distinctions between the personal, the moral, the political and the religious. In the more fundamentalist versions of the creed, this can result in a dangerously illiberal spirit. In more enlightened versions of it, it refuses to carve up reality into separate categories.
Religious faith has social, moral and political implications as well as personal ones. There are, for example, Islamic theologians for whom Islam and socialism are perfectly compatible. Islam began as a religion of the poor, and retains that legacy today. The very word Qur'an, meaning "recital", reminds us that the early disciples of this faith needed its sacred text read out to them, as they were illiterate.
The capitalist West's problem is that it can neither kick belief nor get along with it. It can do neither with it nor without it. It needs some show of faith, not least in times of political crisis, to declare to the world what it stands for.
In reality, however, capitalism is an inherently faithless system. As long as you roll into work, pay your taxes and refrain from beating up police officers, you can believe more or less what you like. Too much conviction smacks of fanaticism, and is bad for business. It is best to get by on as little of the stuff as you can, like a recovering alcoholic.
In this situation, the presence within the West of large numbers of Muslim immigrants is not only offensive to racists. It reminds the West as a whole of the contradiction between its own need to believe and its inability to do so.
Socialists may not agree with the content of Islamic faith, but they are well acquainted by their own history with the idea of millions of ordinary men and women living lives of conviction rather than of pragmatic self-interest. In this, at least, we share a precious tradition with those hounded by the Islamophobes.
Terry Eagleton is a literary critic. His most recent book, Why Marx Was Right, is published by Yale University Press, £16.99 and can be ordered from Bookmarks at www.bookmarks.uk.com