Even in Britain, where communal interaction is making steady progress, religious tensions undermine the efforts of community workers or noble documents like the Parekh report on multiculturalism.
Parliament is asked to curtail historic freedoms in the cause of suppressing "religious hatred". The prime minister, who worked so brilliantly to break down the sectarian divide in Northern Ireland, is inclined to respond to religious differences by endorsing more faith schools, potentially segregating English and Welsh schoolchildren in the same way as Northern Irish. If religion is the opium of the people, then we are high on drugs.
Many of the historical strands lying behind modern religious observance and ideology are covered in Michael Burleigh's sprawling, stimulating book on religion and politics in Europe from the French Revolution to the Great War, a sequel to his earlier analysis of Nazism as a surrogate religion. His text is fascinating, and beautifully produced with superb colour illustrations and rich footnotes. There is a range of enjoyable detail - the symbolism of David's painting of the murder of Marat, Dostoevsky's spiritual turmoil over revolutionary "new men", Wagner on the music of the sublime, Comte throwing knives at his mistress while reciting Homer.
The book covers the more conventional story of the attempt of both Catholics and Protestants to confront the forces of modernisation after the French Revolution drew up new battle lines between church and state, faith and force. As befits a German specialist, Burleigh is particularly strong on the Kulturkampf, the battle of German Catholics against the Bismarckian state. He also covers the conflicts and accommodations of churches with nationalism and socialism, shown in the soul-wrestling of O'Connell and Mazzini, prophets of Young Ireland and Young Italy respectively. There is the even more powerful challenge of urbanisation as traditional religious bodies struggled to survive in the anonymity and disorder of cities. Imperialism should be added to this list.
But Burleigh also has a far more original theme, the mutation of secular creeds into "political religions". Tocqueville saw this in examining the messianic impulse of the French Revolution. Others later applied the idea to modern totalitarianism. Thus the Jacobin Robespierre appears as a highly religious prophet: he condemned the de-Christianising zeal of apostles of the Cult of Reason, and it cost him his life.
Burleigh shows how the trappings, and in part the substance, of organised religion coloured the international socialist movement. In that sense, when Morgan Phillips observed that the Labour Party owed more to Methodism to Marx, he was making a doubtful conceptual distinction. Utopian thinkers - St. Simon, Fourier, Robert Owen, Comte, even Marx - are seen as prophets of a "philosophical religion". In liberal, rational Britain, the emergence of a substitute public morality, focusing on civic and social reform, owed much to the moral canon of churches which were unthreatened by it.
Progressive movements demonstrated man's abiding religiosity. French writers like Lammenais or de Mun extended Catholicism to embrace liberalism and social reform. A German Protestant like Adolf Stoecker adapted his faith to militarism and even anti-Semitism.
Burleigh weaves together a rich miscellany of themes, but his book is less accessible than his earlier masterpiece on the Third Reich. Its very introduction is a complicated statement of what the book is about. And it stops with Pope Benedict XV's ineffective peace moves in 1917: since we have no conclusion, it is not clear where the argument has got us.
The emphasis is always on the enduring importance of religion. We read that in Britain "socialism did not displace Christianity". This is certainly true of ILP evangelists like Hardie and Snowden. But we hear nothing of frankly anti-religious socialists like the Fabians. Burleigh's view of them emerges in an offhand reference to Sidney Webb "worshipping the ghastly Beatrice and the beastly Soviet Union". A throwaway line about the Left's enduring, characteristic "unselfconscious projection of its own conspiratorial imaginings and its corrupt modus operandi" has a man-down-the-club ring to it.
The idea that those who advocated Church disestablishment were intrinsically religious in motivation should be re-examined. That would hardly apply to Clemenceau or Jaures, say. The author, attached to the University of Cardiff, might reflect that Welsh disestablishment, achieved amid broad indifference in 1920, was above all a political statement of national identity against the Church of England in Wales.
But this is only to say that Burleigh has written a thought-provoking, deeply civilised book. Its sequel, eagerly awaited, will examine a world turned upside down by totalitarian political religions, after 32 million men had been killed or mutilated pursuing a Holy War.
Kenneth O Morgan, biographer of Keir Hardie and James Callaghan, has just completed a biography of Michael Foot