Just a word on why supposed holy men would wish to summon demonic entities: In a book I read recently (I don’t recall which, I’ve been doing a lot of reading lately), it was mentioned that as well as other methods, such as sensory deprivation or over-stimulation, utter terror is an effective method for suspending disbelief, shutting down the mundane voice that would otherwise cast doubt upon the operation and render it inert. Fear of divine retribution would certainly suffice for these priests.