Click the Imprimis link to see why D'Souza concludes:
Let me conclude with a warning first issued by one of Western civilization’s greatest atheists, the German philosopher Friedrich Nietzsche. The ideas that define Western civilization, Nietzsche said, are based on Christianity. Because some of these ideas seem to have taken on a life of their own, we might have the illusion that we can abandon Christianity while retaining them. This illusion, Nietzsche warns us, is just that. Remove Christianity and the ideas fall too.