Many people who want to warn against Scientology try to do so by pointing to their mythology, buuuut... I don't think that is quite the right angle, since virtually all religions - including big, established world views that are regarded as "normal" because so many people consider them factual truth - become ridiculous if you take a detached look at their foundational stories.
Yeah, being made aware of Xemu, DC8-starships and volcano-thetans may help to keep *some* people from becoming drawn into the organisation (which is why they don't tell you about it until you are deeply indoctrinated), but sheer ridiculousness does not suffice.
(Otherwise, there would be no Mormons or Hare Krishnas around any longer, just to mention two examples that won't get me penalised around here.)
A more objective angle than the plausibility of their world view comes with their actual practices, particularly the
Office of Special Affairs.
In case you aren't aware, Scientology basically has got its own secret service: a whole branch devoted to investigating, discrediting, and - if possible -
destroying opponents, gaining political leverage, and furthering the organisation's goals by any means possible.
Their "
Operation Snow White" was the greatest infiltration of the US government prior to the Russian meddling in the 2016 presidential election.
You might wonder why they are still around, despite this public knowledge of their more sinister actions. The answer to that is that they are keenly aware of how the US system works: if you've got enough money, you are essentially above the law, and if you know the right people (which comes with having enough money), nothing is beyond you.
They essentially
blackmailed their way to tax-exempt status as a religion in the 1980s, harassing IRS personnel until they gave them what they wanted.
And when Germany tried to fight back against this organisation on account of their anti-constitutional practices and values (which is basically the ONLY thing that can get you indexed around here), US officials were ready to exert pressure on Scientology's behalf, until all opposition was either eliminated or rendered ineffectual. They even managed to gain broad public support by painting themselves as "the next Jews" in widely publicised, expensive newspaper campaigns, raising the ire of the US public.
Some federal states around here tried to push back, but what happened then was usually this: the US consulate sponsored some clandestine dinner or charity event hosted by Scientology, inviting influential representatives such as the chief of police, mayors, etc. Afterwards, funding for anti-cult campaigns would be cut "for budget reasons".