"You don't get rich writing science fiction. If you want to get rich, you start a religion"-L. Ron Hubbard.
The founder's background
Lafayette Ron Hubbard didn't do too well at George Washington University. He finished his first year with a 1.2 GPA, landing him in academic probation, and earned a 1.25 the next year (~1.22 overall) before dropping out. Shortly after leaving the University in 1932, Hubbard led an expedition of fifty students to collect specimens for the University of Michigan and to videotape pirates, from what I can gather. After visiting 3 out of 16 planned ports of call, his expedition fell apart due to financial problems.
His failure continued in 1941 when he entered the Office of Naval Intelligence in a PR role. Somehow, he skipped every rank before Jr. Lieutenant. When the Navy grasped his ineptitude for such a position, he was sent to work on a submarine, where for two days he led a battle against two submarines that no one else could verify ever existing. Of course, he was relieved of command shortly thereafter. He was sent to the Coronado Islands, where he was once again relieved of his position after "performing unauthorized gunnery practice." In 1947, he saw some form of reason and sought psychiatric help from VA.
Beginnings of Scientology
Hubbard wrote an astonishing 138 books from 1933 to 1938 with some adventure novels and his much-more-well known Science Fiction. I've heard that he was classified with some of the greats (or at least published in magazines within a few pages of them), but I can't say anything one way or the other since it's not relevant and I haven't read them.
His most important work was titled, "Dianetics," described as a current scientific guide to mental health, was first published in the magazine, "Astounding Science Fiction," which was later expanded to an entire novel in 1950. Critics of his work included more famous writers such as Isaac Asimov(best known for I, Robot) and Jack Williamson(Asimov's role model).
This creation story is one of my absolute favorites. I could go into depth, but I've got a cartoon that can express it so much better than me. There are only a few things left out that should be expanded upon: When Xenu left the Galactic Confederacy, he used Pyschiatrists to trick citizens into the journey to "Teegeeack," the 'original' name of the planet on which we now reside. This is why Scientologists are vehemently against any form of assistance from psychiatric medication. They instead get their help from "auditors," who use E-meters(which now have been officially proven to do absolutely nothing) to remove clinging Thetans from human souls. As Thetans are removed, human potential increases to superhuman levels(earned at various levels of purity, known to Scientologists as Operating Thetan levels, or OTs which increase with purity), including the ability to stop time, fly, teleport, etc.
With a story like this, you might ask how there are any converts at all. I probably should have warned you prior to that last paragraph that the head of any human below OT3 that is exposed to this information will explode. Well, that used to be the official statement, but when coupled with one of their chief ways of theft, it falls to pieces. Couple that with their personality quiz recruitment tactic (Do you find yourself blablabla? A or B? Regardless of your answers, the auditor explains to the test-taker exactly how screwed up they are and how Scientology is the only way to make the taker better.), and you have an insecure bully who can only grow by demeaning the emotionally and mentally weak.
What takes the cake and what is the most vehemently offensive portion of Scientology dogma is that the E-meter sessions are a paid service to the church:
"Scientologists who are interested in accomplishing the major goals of Scientology -to become Clear and develop their capabilities as Operating Thetans - should expect to be investing heavily in their spirituality. Costs can vary considerably depending upon the needs of the individual, but a rough estimate suggests you'll be paying $128,000 to reach Clear, another $33,000 to reach OT III, and an additional $100,000 to $130,000 to reach OT VIII, which is the highest level currently available." -Altreligion
This would be somewhat accurate if paid salvation was the only method of thievery they employed. After reaching a higher level, the "Church" has been known to claim a clerical error of sorts, forcing an OT to repeat levels and their accompanying payments, allowing a possible never-ending loop of payments.
This is why you're wrong
The journey to salvation, purity, Cleanliness, whatever you want to call it should be an inward journey through your psyche. I don't care if you believe that crab people created the planet from beach sand, but if you are forced to pay for these crab gods to accept you, then there seems to be a problem. If you WANT to give money out of your own free will, that's one thing, but Scientology is like Public Broadcasting: Pay $x and you get a shout out. Pay $y and you earn a duffel bag. Pay a third of a million dollars and you become perfect(assuming Scientology has their paperwork in order).
Religion should be, like Kyle Broflowski said, "all about the message." To take advantage of the curious and confused is one of the more despicable things of which humans are capable of committing. This is why Scientology is a sham, this is why Scientology is a crime against human spirituality, and why Scientologists are wrong.
(source: "Bare-Faced Messiah"-Russell Miller)
(source: OT3 documents via Wikileaks)