That is simply untrue.
A person under hypnosis can be manipulated into to doing things they would not ordinarily do and even have false memories implanted.
To suggest a person is in full control of their will under hypnosis is ridiculous!
False memories “syndrome” and even multiple personality disorder are not induced by the hypnotist. They are not “brought out” through hypnosis.
The subject, or patient, has Borderline Personality Disorder, which if you read more about it, they are desperate for attention and, in that way, in the hands of someone who wants to exploit or control them, go along this “treatment.”
They like the excitement and turmoil that goes along with false memories and MPD. It is now called “Dissociative Identity Disorder” and I believe is iatrogenic and non-existent. It goes away when ignored, and some people have acting talent plus a Borderline Personality and MPD/DID is the result.
I have known people who spent (wasted) years of their lives with this type of thing.
There are scams where someone comes to town, books a hotel ballroom, sells tickets and makes a lot of money from people desperate to lose weight or stop smoking.
The hypnosis I have witnessed was not a silly demonstration, or sensationalistic side show. The two doctors I know explained that hypnosis can only “work” if the subject wants it to. All it is is a relaxation exercise! If you have witnessed anything else from hypnosis, you have been conned by the hypnotist AND the subject.
“If it works, everyone would be using it”-- just like any other psychological treatment, it doesn’t work for everyone. But that is the same as saying, if sleeping made people feel rested, people would sleep every night and wake up feeling rested. Most people sleep-- their brains go into various brain-wave levels of consciousness needed to chemically restore the brain’s systems. Not everyone feels rested by sleep.
As for it being “spiritually dangerous”, that is a state of mind. You have to “allow” it to happen-- it is your will. If you submit your will to another-- and you don’t have to be hypnotized to do that-- you may do things that are not in your character.
What I suspect is far more dangerous are drug induced states of mind.
There have been great saints who went into trance-like states. I would never attribute that to their will being taken over by anyone else.
They are called “mystics” and that is another subject, and completely off track from what the OP asked. I believe the OP was describing the hotel ballroom hypnotism, which is most likely a money making scam with no results.
I take full responsibility for derailing the topic, but I also have studied and experienced this issue and try to correct misconceptions of it.