Is there actually evidence of that stuff happening or is it all urban legend?
It mentions Gilles de Rais if I remember correctly and I understand that he was indeed executed for performing satanic (or occult let's say) rites that involved child sacrifice. However, I think there is now some debate as to whether he did in fact drug, fuck, castrate and murder hundreds of children, or, if the charges were created by his political enemies to get him out of the way.
A similar story to the guy in the Devils of Loudon whose name I forget. According to Huxley, the charges against the priest - which stated that he was knobbing all the nuns while leading them in satanic rites - were completely fabricated and the actual motive was the priest's popularity with the people and his resistance to an edict that towns with fortified walls needed to remove them. This was a big deal cos it changed the balance of power in that if every town had walls France became something like a number of connected semi-autonomous states.
The film adaptation ignores all that and goes straight for bean-flicking nuns and so in, but a straighter film version of the actual book could be interesting too.