I read your argument with interest. You pretty well covered most of my thoughts on the subject. I think there are real problems of how science tackles “subjective” states and it doesn’t seem well equipped for the task at the moment but I really think that this will change even against the will of many. I know the “new age” argument that science hasn’t yet found the tools to measure or theories to cover various phenomena that are anathema to it is weak but it may well be true despite that. That all things scientific are testable is debatable; Yes we can hear the echoes of the big bang (a theory currently accepted faithfully by many in the scientific fields), but of course it is quite possible that a new theory of the origins of the universe that is different can arise and explain these echoes as some other measurable manifestation of that theory. It seems to me there are huge shifts appearing in science (“the new paradigm”) as scientists capable of being truly sceptical note the superstition (past) science (present) science fiction (future) progression of their ideas and the level of faith implicit in them. 

Of course all states of mind are drug induced; “Normal” covers a huge range of mental states mediated by seratonin, melatonin, endorphins, adrenaline, anandamide, dopamine, GHB, DMT etc. etc. As “sentients” were all damned to be holistic drug users; we could just chuck everything into a box labeled “subjective” & be done. I think there is a huge amount of useful work to be done in neuroscience and other fields with psychedelics but we are really just at the beginning of this. The whole idea of psychonautics as it is developing seems to present consciousness as a new natural science and despite the mystical overtones most seem multidisciplinary in their nature. It seems to me multiple realities are strongly implied by and underpin much of science.  

As for psychedelics, I suspect that although there are many scientists who believe the negative propaganda, there are quite a lot of scientists who would like to work in this area still, but the area is of course controversial and frowned upon by those who have control of funding and the like.  Apart from above board organisations like MAPS, there are scientists who are doing this kind of research quietly on their own anyway and works like the Entheogen Review suggest that the laity are getting rather more clued up and beginning to fill this deficit as well.