Yeah, many if not most people do psychedelics solo/with friends, it's rare to have an actual tripsitter, usually that is done in cases of psychedelic therapy for example.
I understand the sentiment, I'm not religious either - so I personally don't view the shaman as a priest or in contact with supernatural powers or anything of that sort, but as a guide with practical experience in these settings as well as working with the drink itself.
Well, I haven't memorised people's bad trip reports, but generally the stories go scary. Hell realms of magnitude I daren't speak of. Not that this can't happen in a ceremony, because they certainly do, but there the experienced guide can lead you out of it, ground you, help you in many ways that you won't possibly be able to do for your self on your own. The Aya brew is one of the most potent substances around and is a tool, not a toy to be played with for entertainment sake or the like. Basically, it demands respect and proper care to have beneficial effects in the long run - and not a mental ward hospitalisation in stead.
- Also, sorry if this is spamming your thread, OP!