Although defenders of religion like to portray faith as a source of peace and fellowship, and condemn those who commit atrocities in its name as untrue believers, the daily news media show how far this is from being invariably true. In fact, the relentless drip of bad news about religion-prompted violence in the world shows that the more zealous people are in their religious beliefs, the more likely they are to behave in non-rational, antisocial or violent ways.

The cold-blooded public murder of soldier Lee Rigby in Woolwich this week is an example. Murders are committed for a variety of reasons, but one thing they have in common is that those who commit them have to be in an abnormal state of mind. From rage or jealousy, through the cold psychopathology of the professional hitman, to the soldier who must be rigorously schooled and disciplined so that he can kill other human beings in defined circumstances, a difference to the normal mindset is required. One potent way of achieving the required mindset is religious zealotry.

Belief in supernatural beings, miracles and the fantastical tales told in ancient scriptures is, at least, irrational and, at worst, pathological. Themore earnest the belief, therefore, the less sane is it likely to be in its application to the real world. At the extreme, it not only prompts but also – from their own perspective – justifies believers in what they do. Unnatural lifestyles, self-harm, ritualistic repetitive behaviours, fantasy beliefs and the like – all of them the norm for religiously committed folk – might be harmless to others in most cases, but when they become annexed to hostility to others outside the faith, or to apostates within it, the result is dangerous.