This is a really interesting topic
I have no issue with drugs - no moral stance on them. They can be used both skillfully and unskillfully.
But when I hear people advocating quite strenuously that they are useful for moving forward on the Path, I think that in 99.9% of cases this is not true.
Mostly I think that there is a profound misunderstanding of what Samadhi is and what it is used for. If one relies on psychedelics to loosen up the normally concrete-hard conceptual processes of the mind - it is just an external experience. There is no insight into how the mind works. What happens is that View conditions perceptions and interpretations of the experiences. Without Right View, the interpretations are not in line with the Dhamma. The problem becomes that people are so convinced by the experience that they believe that what they have ‘perceived/interpreted/fabricated’ is the Truth.
This is the opposite of the way Samadhi works. Samadhi allows one to penetrate that ‘what one perceives’ is NOT the truth. It leads to understanding, wisdom and letting go. Once one has seen that Samadhi is conditioned, and understands the processes, then one begins to see with clarity and break through delusion. I believe that psychedelics lead to greater delusion. Now they may feel great and they may be useful in certain contexts for certain people, but the results should not be confused with the Path of Practice.
There is also the position that if one is led by someone who has Right View, then they can be led to a range of insights. Well this is ‘better’ than being left to whatever view the person has, but still then this experience is entirely constructed/fabricated by the leader (are you positive they have Right View?). It gives the interpretation of the experience and the person may believe it… But again instead of highlighting the impermanence, and not self nature of the mind, of penetrating the depth to which conditioning and Dependent Arising create our world, there is the assumption of some kind of reality and Truth… something that is accepted as real - after all one has EXPERIENCED it for oneself, how could one have doubts any longer?? That is the problem. Instead of resulting in Nibida (unsatisfactory, impermanent, unreliable, subject to grasping) for how the sense bases and consciousnesses work, it makes one feel that one has had access to ‘the real truth’.
Having a psych background I’ve always been interested in these things. Indeed, hearing more and more about the current wave, I even took some for an experiment a little while back to compare the effects of it with Samadhi. My impression can be described by a simile. Say that our conceptual mind is encased in hard wax, the psychedelic serves to soften that wax somewhat. SO the conditions and View at the time of the experience is what completely determines what is perceived - good trips, bad trips etc etc. It was interesting with the visuals, it was like eye consciousness became detached and just did its own thing separate from the functioning of the (internal/external) sense base of the eye - quite irrelevant, interesting sort of but - meh…
With regards to the joy that many people talk about experiencing- it was certainly there, but it was nothing like the bright pure joy from samadhi, it was ‘dirty/hazy’ sort of smokey dull… Perhaps if one had never experienced anything like it, it might be very attractive (maybe even feel transcendent compared to the experience of daily dukkha) - but really not much compared to Samadhi. It also leaves one with a ‘hangover’, rather than the pure energy, brightness and clarity of samadhi. I won’t ever be taking it again, it’s just totally not worth it. But the experiment was worthwhile. It enabled a comparison rather than just theorizing and propounding ones own position.
My own belief is that people for whom samadhi does not come easily, or at all, sort of convince themselves that this poor facsimile somehow is a legitimate replacement for it. I cannot imagine that if anyone had a choice between samadhi and a psychedelic trip that they would ever choose the latter.
The sad thing is that, IMO, as a result they are putting in the conditions that will make it harder to get to samadhi… Chasing what appears to be a good short term option, or a short cut, they hinder the conditions for proper development of Samadhi.
Of course for those using it in a therapeutic manner, for ordinary people not on the Path, it can be of benefit.