People are sometimes distressed by the bare knowledge that lifestyles are being practised or opinions held which they take to be immoral. Is this distress to be regarded as harm for the purposes of Mill's Harm Principle? I argue, first, that this is an issue that is to be resolved not by analysis of the concept of harm but by reference to the arguments in On Liberty with which the Harm Principle is supported. Secondly, I argue that reference to those arguments makes it clear beyond doubt that, since Mill valued moral confrontation and the shattering of moral complacency as means to social progress, he must have regarded moral distress as a positive good rather than as a harm that society ought to intervene to prevent. Thirdly, I relate this interpretation to Mill's points about temperance, decency and good manners. I argue, finally, that my interpretation is inconsistent with Mill's underlying utilitarianism only if the latter is understood in a crudely hedonistic way. [ABSTRACT FROM AUTHOR]