I don’t at all agree that those who are sceptical about it are only so because it “didn’t work for them”.
If it was all just relaxation and breathing techniques and knowing about the process of birth, then that’s absolutely fine - no problem with that at all. What tips it into snake oil IMO is the “hypnosis” claim. Hypnobirthing quite explicitly doesn’t say it’s just about relaxation techniques - the entire point of it is the claim that you can induce self-hypnosis. And a large amount of that rests on whether you (a) believe hypnosis exists and (b) whether you’re particularly suggestible or susceptible to it (and the whole idea).
Now, I can’t pronounce on whether hypnosis exists. But I’ve had several people (including a hypnotherapist) try to “hypnotise” me in other contexts, and it didn’t work on me in any respect. Either I’m not suggestible in that way, or whatever; but in the hypnobirthing course I did (leaving aside the course leader’s dodgy medical claims), the breathing and meditation exercises were great; but none of the supposed “hypnosis” or “self-hypnosis” did anything for me - CD, visualisations, no hypnosis going on.
Now maybe others are more amenable to it, or whatever. I don’t know - I gather that hypnosis does seem to work for some people. But just as like in stage hypnosis acts, the entertainers do sone routines first to find the people in the audience who are most amenable/suggestible, I suspect that it might just work for some people better than others. (If hypnosis exists, that is.)
However if all it is is breathing and relaxation exercises, well, there are situations in north where no amount of those are going to help. I had an induction that went wrong, continuous contractions and a hypertonic precipitate labour when they were trying to stop involuntary pushing - I couldn’t even catch my breath never mind do a visualisation!
And I was terrified out of my wits because I knew quite well what could go wrong and what was happening, and no amount of relaxation exercises was going to stop me knowing what was going on, especially when they pressed the big red button.
Whereas for women having a straightforward birth with normal contractions, breathing and visualisation may well help enormously. Also if everything around them is encouraging and calm. Whereas, it’s pretty hard to go into yourself, focus and breathe with the surges if there are midwives and doctors running around yelling for assistance with looks of terror on their faces 