Not that there's anything wrong with devil worship...
I do, however, agree that it is a bit of a stretch to call it entertainment, especially if they believe that what they are experiencing is real.
To those of you who find it reasonable to allow people to believe that they are actually contacting spirits (relatives or not), how would you answer if someone came up to you after your presentation and asked you man-to-man if it was real? Anything other than the truth, to any degree from "it's a trick" or "it's psychology" to explaining the whole thing, feels wrong to me.
And there is a slight contradiction in the justifications of those who allow people to believe; they say that people would keep their belief regardless of exposure AND that by exposing the truth, they'd somehow be hurting the person. Regardless, I think people can handle the truth, or your openness about there being psychological trickery, if you present the truth the right way. Stating, "It was all a trick and you're all stupid for believing it was real" will obviously offend them, but if you approach the reveal with sensitivity, I'm sure you can get some people to acknowledge and perhaps appreciate that they can be deceived (or deceive themselves). Jerry Andrus would tell his audience something along the lines of, "The reason I can fool you is because you're all intelligent human beings. You trust me and what I say and I can exploit that if I so desire. You take small things for granted because in day to day life, you have to. That's a fine, normal thing, but sometimes, it can be manipulated."
Following that, if you reveal the psychological and physiological trickery (while keeping it light, fun, and sensitive), people would both give you credit for your cleverness and walk away thinking. Only the extremely thin-skinned would take offense. Regardless of the conclusions they reach later on, at the very least you won't be lying either explicitly or by omission. Making them aware of the deception and cognitive dissonances involved in what felt like a very real experience, and giving them a lot to think about when it comes to their perception of the world-- that is entertaining.
Teller's introduction to Psychological Subtleties argues strongly in favor of such an approach. It can turn charlatanism and, as Penn would call it, "Jive-*** BS", into actual entertainment.