I had my back tatoo being done on 4 sessions, each was 4-hour long experience. It felt as a pizza cutter running here & there on my back, having areas around spine and sides much more sensitive and thus painful. I can guarantee you, after coulpe of hours of nearly-sustained pain, I was dumbed down to basic creature, which can say yes, no, left, right and that was about it. Imagining 2 years of it... you, not even me, have an idea how crippiling such pain long term is. I can see roughly your point - but it's a point made by boy who has no clue how crippiling constant pain is. Neither do I, but I had at least a glimpse. With pain level high enough, it would cripple your remaining days to drooling struggle to function like a human being. That's why most of those unfortunates end up on high doses of painkillers, which really dumb them down to semi-consious level. That's not what psychedelics do to you.