Father Jeremy Davies, a priest in the Westminster diocese of the Catholic Church of England and Wales, is claiming that sexual promiscuity makes a person more vulnerable to demonic possession. In his new book Exorcism: Understanding Exorcism in Scripture and Practice, Davies says that sex is a holy activity that should only be pursued within the confines of marriage. Open your bed (or back seat, or empty elevator) to just any old somebody, and you're also opening your soul to a wandering demon. Homosexuality, he says, can be caused by a contagious form of demonic possession. I'm not sure by what mechanism this theory works--whether, for instance, the devil spirits enter your mouth during orgasm--but I'm sure there's some kind of scientific explanation for it. After all, Davies' book is published by the Catholic Truth Society, which is on the cutting edge of both rationality and oxymoronic naming. More details here.
