Jesus did indeed 'cast out devils' (probably dealing with the mentally ill) but never by means of physical violence, torture or abuse. He merely commanded the 'demon' to depart. The Gadarene swine ran over the cliff of their own accord, I don't remember Jesus telling them to do so.
It's quite true that peoples with a primitive mindset, (NOT a racist comment!) and living in abject poverty, are very easily exploited and manipulated for gain. They seek (in my limited experiences in Africa) to explain the myriad misfortunes which beset them in supernatural terms. Thus any wicked person looking for a means to make money can pretend to 'know' the source of the 'sorcery' and this is implicitly believed. My husband's poor mother, a devout Muslim, took her dying son Suleyman to a 'marabou' (a kind of witchcraft/sorcery exponent) and paid him her last few coins, He affirmed that someone had put a spell on the boy, and maintained he could remove it. Later the boy's conditon worsened and his father took him too the local (paying) hospital. No-one is admitted there without payment, but they had nothing, so joined the folk on their knees in front of the passing doctors, literally begging and clutching at their white coats for their help. No doctor responded, and the boy died there on the floor after THREE DAYS of agony. (It sounded like palcifarum malaria, he was delirious and screaming with the pain in his head. He was fifteen years old.) I tell this true story to illustrate the dire conditions in some places, and the desperate beliefs and practices resorted to. Faced with this need, the 'witchdoctors' and 'exorcists' have the people in the palms of their hands. If they promise to 'remove the evil' some folk will accept any bizarre or extreme 'remedy' and pay handsomely for it. So poverty and ignorance (those two fearsome children in 'A Christmas Carol')are to blame, and not religion per se.