At a Vatican conference talking Evil

"If one is addicted to something, it allows the evil spirit to hook into that and make it more potent," said one of the British priests. 

He has only been involved in one exorcism, in which a woman in her mid-40s spoke in a deep, growling voice. Cases of true demonic possession were rare. 

“A considerable number of the cases referred to us are in fact psychiatric cases,” he said.

During the week-long course, there will be lectures by Catholic prelates on subjects such as “Occultism, black magic and Satanism”, “Angels and demons in Holy Scripture” and “Criminal Aspects of Satanism”.

I think both original sin and Satan exist, which is actually a very rational thing to believe in at times, given the utter evil that exists in the world.