In a blog entry about European anti-Americanism a few days ago, Nelson Ascher recommended Norman Cohn's book Europe's Inner Demons about the Great Witch Hunt.
Thanks for pointing that out. I've read Europe's Inner Demons -- I think the thing about it that stood out most in my mind is that Cohn's research showed that the impetus to witch burning came not from peasants, but from the intellectuals of the day, and secondly, that its roots were planted firmly in the Renaissance (and later in the Reformation and to some extent the Enlightenment) but not in the Middle Ages. Ascher does a good job though of summarizing Cohn's argument.
Some of the descriptions of the injuries European witches were supposed to have caused are consistent with poisoning. (Miscarriage, cows
ceasing to give milk, impotence, etc.) (FWIW, in West Africa poisoning someone is considered one form of witchcraft.*)
I'd suspect that the power of witchcraft didn't lie entirely "in the power of the victim's beliefs."
(*)Harley wrote that learning the basics of poisoning and antidotes was part of the Sande Society training, so perhaps their hatred of witches is more a function of the witch's goals than their means.