One of the big differences, and a big pointer to Scientology being a massive scam, is that with Christianity you are totally free to go buy a copy of the book containing the complete belief system. I might believe that in its own way Christianity is as silly as Scientology, but I don't have to pay a fortune and work my way up inside the church to find out what those beliefs are. They're open and honest about them, and dedicated to sharing those beliefs with anyone who is interested. If someone is trying to sell you salvation, or telling you that they have the truth, but you can't have it until you've handed over your cash, or until you're ready to handle it, then that person is trying to take you for a ride.
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