In many Western cities, plans to erect mosques often stir more passion than any other local issue—and politicians are leaping into the fray. NOT since Cologne was rebuilt half a century ago, out of the rubble of war, has a change in the urban landscape generated so much heat. A city whose main landmark is a medieval cathedral may soon share its skyline with another place of worship: a large mosque with minarets more than 50 metres (165 feet) high. While the city's (mainly Turkish) Muslim population of over 120,000 is looking forward to the new building—a sign, perhaps, that...