It seems to me it was the early wave of psychonauts, who tended to be a very spiritual lot and viewed psychedelics as sacraments and frowned upon recreational use without some sort of inner or outer exploration. You can see it in the early trip reports on Erowid, which is what subsequent generations used to learn about tripping, and they looked up to those early explorers. Unfortunately a lot of those people were pretty elitist about it, when I came to PD there was a whole contingent of old-school trippers, who were just really assholes, shaming everyone who used psychedelics to party or have a good time, shaming high school kids who'd come on and ask a basic question, etc. It was ridiculous. But yeah I think that's where the idea of "rules" came from. I think since then most people have realized that psychedelic use is a personal thing, it's what you make of it, they're not some divine sacrament, but you can view them that way and use them that way and that's cool for you, or you can use them primarily to have fun, whatever, nothing wrong with that. It's up to you. Personally in my early days I had some immensely profound and life-changing experiences and I tended to view them as sacraments, but as I've gotten older I now mostly use them to enhance certain activities such as hanging out with friends, listening to or playing music, and seeing live music or going to festivals. Sometimes for a good camping trip or day hike too. I don't go for world-shattering experiences anymore, because I've been there, I don't really need to go back, I've gotten the message several times over. But I don't necessarily agree with the old adage "get the message, hang up the phone". psychedelics are tools that have many possible applications, and I find that the way I use them now still brings beneficial value to my life, so I continue to use them.