I'm not too sure about that Enthetan. Joining the Sea Org was very much a one-way transaction (I know, I did it). You didn't have to join the SO to do the OT levels. People who joined learned that they received very little in the way of training and processing but instead found themselves scrubbing decks with a toothbrush or spending time in a chain locker.
I like Enthetan's point. It's like, who better to define satanism than people who believe in it's existence and have a comprehensive and historical understanding of what it means. I suppose when talking about satanism we could go way back to pre-Christian times but in today's context aren't we talking about Christianity vs paganism? To a Christian, if it walks like a duck and quacks like a duck...
And there certainly are an awful lot of things about Scientology that fit that description. It's true than non-Sea Org Scientologists haven't signed the billion year contract but their money pays for other people who have. Lots of Sea Org members route out and continue to be active true believers. As you say, very rarely do Sea Org members get the auditing and tech training they are promised. To a Christian that is probably comparable to being a second class satanist - studying lot's of satanism and helping other people meet satan but not getting to participate in the conjuring and sacrifices yourself.
Scientologists live in fear of many things but paramount among those things is the threat of losing access to the Bridge, auditing and training because they believe it is the only way to salvage their spiritual eternity and to save the planet and all of humanity. If they don't go clear and OT then they are doomed to wander the universe as lost souls in an eternal downward spiral of degradation and unconsciousness. Forever lost will be the chance to regain their original abilities to read minds, go full perceptic exterior at will, levitate ashtrays, strip away whole planet's atmospheres, zap each other with tractor and pressor beams, have full whole track recall and consciously pick your new perfect body and rich IAS statusy Scientology parents.
I think it's fair to assume that Christians believe only God has the power to grant these things and anyone else who promises it is a deceiver, a minion of evil selling a wrong path that leads to Satan. We can argue that both Christianity and Scientology are just pushing their own versions of religious monopoly but that doesn't let Scientology off the hook for meeting the Christian interpretation.
And Scientology paints Christianity as it's own version of hell. It's just all the dramatization of whole track implants intended to keep us from finding Scientology, the only workable spiritual technology or to make us destroy it if we do. Bet they don't put that it the Interdenominational Brochure.