Perhaps, if as you say there is no argument that will enlighten these people, one should consider whether the scriptures and teachings they work from are a danger to themselves or others. I have sympathy for those involved in Scientology, dianetics teaches them that most ills are psychosomatic, that homosexuals are perverts and very phsyically ill (from the book, not from a website). However I do not read about Scientologists commiting murder in the name of LRH, becoming suicide bombers in the need to rid themsleves of Thetans and the like.
I will continue to try to understand how seemingly rational people, for I know many, become involved in such an obvious scam. For a religion that claims to be scientific fact based it has a unnatural adversion to the scientific community. Even a skeptic like me should be able to 'see' the proof if they are correct.
Who knows perhaps they are - what a scary thought!