Richard Beck pulled out this (timely?) quote from Mere Christianity
Finally, though I have had to speak at some length about sex, I want to make it as clear as I possibly can that the centre of Christian morality is not here. If anyone thinks that Christians regard unchastity as the supreme vice, he is quite wrong. The sins of the flesh are bad, but they are the least bad of all sins. All the worst pleasures are purely spiritual: the pleasure of putting other people in the wrong, of bossing and patronising and spoiling sport, and back-biting, the pleasures of power, of hatred. For there are two things inside me, competing with the human self which I must try to become. They are the Animal self, and the Diabolical self. The Diabolical self is the worse of the two. That is why a cold, self-righteous prig who goes regularly to church may be far nearer to hell than a prostitute.
–C.S. Lewis, Mere Christianity