According to the most influential contemporary reading of John Locke's Letter Concerning Toleration, his main argument against religious persecution is unsuccessful. That argument holds that coercion is ineffective as a means of instilling religious beliefs in its victims. I propose a different reading of the Letter. Locke's main consideration against persecution is not the unsuccessful belief-based argument just outlined, but what I call the sincerity argument. He believes that religious coercion is irrational because it is ineffective as a means of (...) inculcating the right intentions in people. Once this alternative argument is placed at its centre, the Letter is seen to be a more fertile source of political argument than is suggested by alternative readings. In particular, the sincerity argument gives us a powerful reason for rejecting state moral paternalism, the doctrine that the state may use coercion to make people morally virtuous. If moral virtue depends upon people having the right intentions, and if coercion is ineffective as a means of instilling the right intentions in people, then state moral paternalism is ineffective and hence irrational. (shrink)