I agree with you that this feels like exploitation. However, I've seen several references on this site, though not lately, to the desirability of betting play money or small amounts of real money on one's beliefs, as a way of "keeping oneself honest." I like this principle and engage in small bets with other people on occasion. Is your problem here with the amount of money changing hands, with the massive advantage to one party, or with the concept of betting on beliefs in general?
I have a problem with taking advantage of people based on their delusions. If a dude thought he was Napoleon and was entitled to Napoleon's old swords, would you:
1) Offer to sell him fake swords that you claim to be Napoleon's (assume he wouldn't know the difference)?
2) Attempt to explain to him that he's not Napoleon and he shouldn't be seeking the swords?
3) Find him professional help?
4) Do nothing?
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Providing assurance that pets will be provided for in the event of Rapture.
Having thought it over, I'm OK with the ethics of this service.