Norman Cohn's "Europe's Inner Demons: An Enquiry Inspired by the Great Witchhunt" is a seminal book in the study both of medieval heresy and the witchcrazes. Cohn examines the origins of the Reformation-era witchcrazes, which began toward the end of the 15th century. Cohn's thesis is that the accusations later made against witches originated in second century accusations against Christians by the Roman authorities. He traces these early stories to accusations against heretics from the 11th to 15th centuries and finally to accusations against witches. They persisted because they effectively tapped into latent European fears that did not change or dissipate with the transition between paganism and Christianity as dominant religions in Europe. Cohn does not deal with Islam, but the relative lack of obsessions with witches in contemporary Islamic countries is perhaps instructive. Though this also could be a question of region rather than theology. The witchcrazes were especially virulent in Northern Europe.
Cohn's book came out in 1975, so technically, it should be getting very obsolete at this point. His connections now appear a bit tenuous over such a long period of time as medieval historiography moves away from the "long view" approach to history. It is true, as well, that Cohn doesn't really make a strong connection between the second-century accusations against Christians and the much later 11th-century accusations against heretics.
Yet, Cohn's book has become a classic in the medieval historiographical field that remains relevant for two reasons. First, it's difficult to argue with the comparisons that Cohn makes between these different outbreaks over time. Second-century Christians were accused of ritual cannibalism involving babies and secret sexual orgies (something that Cohn attributes to a misunderstanding of the symbolism of early forms of the Mass). So were 12th century heretics, the Templars in their early 14th-century heresy trial and the later witchcrazes. Cohn's argument that these charges reappeared after only sporadic usage in the 11th century as part of the tide of millenarianism also makes sense. Millenarianism jacked up the anxiety of the times considerably as Europeans prepared for the End Times. Therefore, it would have brought back into relief latent anxieties in the European consciousness.
Second, Cohn does an overview of the historiography up until 1975 and shows the shakiness of two popular theories in particular: the midwife holocaust theory and the paganism survivals theory. The first portrayed the witchcrazes as a misogynistic holocaust against women, especially women healers like midwives. Cohn disproves this theory by showing that many accusations of witchcraft were in fact made not by men, but by women against other women, usually by the loser of a court case. The paganism survivals theory portrayed the witchcrazes as an attack on pagan European practices that had survived since ancient times. But if Cohn's theory that the charges were first levied by pagans against early Christians is true, this theory cannot hold, either. Even if Cohn's basic theory is wrong, the paganism survivals theory cannot explain why such charges were also leveled against medieval heretics who were almost always fundamentalist Christian groups seeking reform or a more "primitive" Christianity than the Church provided in their time. It would be like saying that suspicions of Mormons or Jehovah's Witnesses reflect paganism survivals in modern western society.
But as this week's film review shows, whatever set people off, the continuation of witchcrazes may have had as much to do with power and money as anything else.