There is nothing in the law of unintended consequences that dictates such consequences must be unpleasant ones (though that’s the way to bet, as Damon Runyon remarked of Ecclesiastes 9:11). An unintended and beneficial consequence of the London bombings is the transformation of the debate in Britain over multiculturalism and “Britishness.” The discovery that the original four bombers were cricket-playing native sons of Yorkshire has alarmed people who had reasonably assumed that the children of Muslim immigrants would assimilate to “Britishness” as a natural result of growing up in the country.

The bombings on the London underground shocked everyone out of this complacency, at least temporarily. None of the usual explanations seemed to apply. The bombers were not poor; they were not “marginalized”; they were not from disturbed or broken homes; they were not living in a culturally separate wor ...