They once plotted insurrection in Britain. Young, middle-class, and angry, they were the vanguard of a generation of disaffected Muslims that, at its most extreme, gave rise to the July 7, 2005, transportation bombers. But now, in one of the most visible assaults on political Islam from within the British Muslim community, a network of ex-radicals launched on Tuesday a movement to fight the same ideology that they once worked to spread. The Quilliam Foundation – named for a 19th-century British convert to Islam – aims to propagate a tolerant and pluralistic view of Islam among young Muslims who are...