John Stuart Mill, proud of his logic, gave liberalism's 1859 answer, maybe the answer of Britain's Liberal Democrats today. He gave it in his principle of state intervention in his essay On Liberty . The principle was that the state is to intervene in the lives of citizens not to help them, but only to prevent them from causing harm to one another. Then Mill didn't say what harm is. Nor did he give it in his essay Utilitarianism, where vagueness about unhappiness and happiness went with an obscure paean to individualism. The vagueness and obscurity helped conceal the fact evident in clearer utilitarianisms, such as Jeremy Bentham's, that they justify having a slave class in a society if that does in fact produce the greatest total of happiness or satisfaction for the society.