The culture of America is always under siege. Countless new arrivals have transformed American culture over the generations. Muslims from places as diverse as Morocco, Albania and Malaysia will change American culture, too. Whoever follows them will change it again. The idea that a handful of Islamic radicals can destroy a nation of 300 million people protected by the world's largest military is absurd. But questions about the Muslim world and its intentions toward the United States deserve answers, and I don't mean the ignorant rants polluting cyberspace. Fortunately, we have Karen Armstrong, a former Roman Catholic nun and an...