To most Western ears, the very idea of punishing heresy conjures up a time four or five centuries ago, when Spanish inquisitors terrorised dissenters with the rack and Russian tsars would burn alive whole communities of ultra-traditionalist Old Believers. Most religions began as heresies. Today the concept of “heresy” still means something. Every community built around an idea, a principle or an aim (from fox-hunting enthusiasts to Freudian psychotherapists) will always face hard arguments about where the boundaries of that community lie, and how far the meaning of its founding axioms can be stretched. But one of the hallmarks of a civilised and tolerant society is that arguments within freely constituted groups, religious or otherwise, unfold peacefully. And if those disputes lead to splits and new groups, that too must be a peaceful process, free of violence or coercion.