system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is scientology and why is it bad?
gpt
Scientology was invented by science-fiction author L. Ron Hubbard and extended out of an earlier work of his called Dianetics.  Dianetics was sold as a method of understanding the body and mind.  It's not a science-fiction book but isn't truly factual either in that the techniques have not really been scientifically studied under controlled conditions.

Hubbard created a spiritual story incorporating Dianetics principles and began offering it as a religion.  He offered a number of stories to explain the origin of the universe, the earth, humans, and how natural and supernatural forces work together and can be harnessed.  There is an allegation that Scientology was invented on a bet between Hubbard and fellow Sci-Fi authors where Hubbard maintained that running a religion was a great way to make money and assume power and influence because laws concerning religion in the United States largely allow religions to do what they want with little governmental oversight or interference.

As with any religion, the concept of Scientology isn't necessarily good or bad.  Scientology does seem to have two issues that cause the greatest controversy.

The first is an expectation that its followers will surrender their entire lives to the religion and its leaders' authority.  Scientology followers are rarely allowed to associate with anyone outside of the religion and outside influences are discouraged.  This helps to preserve control over the followers.

The second issues is that Scientology followers can end up spending a lot or all of their money in pursuit of attaining higher levels of understanding within the organization.  The richer someone is, the higher they can advance.