Scientology states that it is compatible with all religions, though a number of the "secret" doctrines and scriptures of L. Ron Hubbard contradict these statements. Of all the inner workings of Scientology, the most secret and the most volatile documents are the Xenu writings of OT III (Operating Thetan Level III), which detail the origins of human behavior according to Hubbard. The participants at Wikipedia, the free encyclopedia, have compiled an exhaustively researched examination of the Xenu writings, their meanings, and their importance to the religious aspects of Scientology – and its compatibility with other religious beliefs. A two-page summary of the Xenu writings is also available for public distribution, entitled The Xenu Leaflet. ("Xenu" has been spelled Xemu a few times, but it's usually spelled "Xenu.")
The story of Xenu has been exposed far and wide, especially recently, and Scientology spokespersons have tried to rationalize it by comparing it with Christianity. If we’re crazy enough to believe in angels and devils, then what’s the difference between that and Xenu? The appeal of Xenu (especially to critics of Scientology) isn’t really rooted in the (lousy) science fiction story of the Galactic Confederation itself. The real reason why Xenu is such a hot button in the war between Scientology and critics is because Scientology has gone through ridiculous, insane lengths to keep Xenu a secret. They attacked the Internet critics, shut down the famous Penet remailer, tried to ruin the newsgroup alt.religion.scientology, got federal marshals to raid the homes of the more vocal critics, and filed lawsuits against the Washington Post, Netcom (now part of Earthlink), and the Dutch ISP XS4ALL because of Xenu. They’ve spent millions trying to get all references to Xenu out of the media and the Internet. The critics love bringing up Xenu especially because it’s such a big secret.
As best as I can tell, Scientology’s rationale to keep Xenu a secret is because of their belief that OT III can only be delivered to Scientologists in its “original form” (i.e. L. Ron Hubbard’s writing and nothing else) in order for it to work. The wide exposure of Xenu has tainted the minds of those who’ve read the story, and they are less likely (or unable) to accept OT III in its pure, unsullied form because of this. Critics, on the other hand, state that Xenu is so ridiculous and so unbelievable, most rational persons would walk away laughing if they knew that all the time, effort, and especially money invested in Scientology courses and training eventually leads to Xenu.
Personally I agree with the critics: it’s a ridiculous story, and it’s proof of how far out of touch with reality Hubbard was by the time he “broke through the wall of fire” and discovered Xenu. Yet, I also sympathize with Scientologists who honestly believe the critics are out to “destroy” their religion by exposing its secrets to ridicule.
– With apologies to Mystery Science Theater 3000