'Most of the evil in the world is done with the best intentions', said TS Eliot. And 9/11, the guillotine, and the Inquisition were inspired by those who thought they had the highest moral principles. Many philosophers have concluded that morality is a subjective human invention. Should we then simply encourage and argue for acts we support and do without morality altogether? Or is the authority of morality the tenuous thread that holds society together?