Here's a thought experiment.
Suppose that, millennia ago, a handful of people had genuine mystical insights as a result of near-death experiences, deathbed visions, or states of extreme physical or emotional distress. As word of these experiences spread, other people tried various ways to induce such experiences at will. Finding that certain plant products could bring about altered states of consciousness, they concluded that these altered states were the equivalent of the "real" experiences they were seeking.
But ... they were wrong. The real visions, which were (and are) exceedingly rare, just can't be reproduced on demand. And over the centuries, the drug-induced visions became indiscriminately mixed up with the much rarer genuine visions, creating confusion and leading spiritual seekers astray, just as outcrops of fool's gold can mislead prospectors.
If this is the case, how could we possibly distinguish between real visions and counterfeit visions - between gold and fool's gold? We might start by noting that NDEs and deathbed visions seldom seem rooted in paranoia and fear, while drug-induced visions frequently do. To my knowledge, NDErs never encounter grotesque humanoid alien insects, but a remarkable number of DMT users have seen such beasties. I don't think NDEs or deathbed visions involve the kinds of visual phenomena that LSD users routinely report (e.g., swirls of color, "breathing" walls, synesthesia). And so forth.
So if we're going to assume that NDEs and deathbed visions are probably genuine spiritual experiences (in part because of their sometimes compelling veridical components, and in part becayse they dovetail with channeled material from apparently reputable sources), then it seems at least arguable that, for the most part, LSD trips, DMT experiments, and other such practices are counterfeit spiritual experiences.
This way of looking at things is not necessarily correct, but it could fit the facts.
A rebuttal would be that some NDEs and deathbed visions are scary, just like bad drug trips. This is true, but only in a minuscule proportion of reports. When Nancy Evans Bush wrote a book about unpleasant NDEs, she could only find a handful of cases, and even some of those don't sound particularly hellish (e.g., simply floating in a void). Maurice Rawlings, the one investigator who insists on a high proportion of truly hellish NDEs, seems to have pushed this position to advance his evangelical Christian beliefs. Other researchers have not been able to reproduce his results, and there are accusations that Rawlings distorted his data.
In short, while undoubtedly there are some scary or negative NDEs (as well as deathbed visions - e.g., the dying vision of the Emperor Augustus, if it has been reported accurately), the vast majority of cases appear to be positive. The same is emphatically not true of drug trips, which are often frightening, upsetting, even panic-inducing, and may promote feelings of paranoia and despair. It took years of effort for Nancy Evans Bush to find even a few well-documented hellish NDEs. It's not at all difficult to find examples of bad drug trips. As Rosie O'Donnell would say, "Google it."
Here are five bad LSD trips ... a mushroom trip with lasting ill effects ... a peyote trip with devastating consequences ... a scary DMT trip ... another really bad DMT trip ... and don't forget about the DMT "insectoids"! I found all those references, and dozens more, in a few minutes of Googling for the term "bad trip" + the names of particular substances. I could easily link to hundreds, perhaps thousands, of cases. Meanwhile, it's doubtful there are more than a dozen or so well-documented hellish NDEs, if even that many.
The fact that drug trips can go bad does not, in itself, prove that they're a false path to spiritual insight. But the fact that such a large percentage of drug trips go badly, while only a trivial percentage of NDEs and deathbed visions are scary or nightmarish, suggests to me that there is a fundamental, qualitative difference between the two kinds of experiences. And if they are qualitatively different, it's certainly arguable that one set of experiences is largely genuine, and the other set largely is not.
It's always tempting to think there is some shortcut to spiritual enlightenment, and for millennia, many sincere seekers have used psychedelic substances as such a shortcut. But maybe, just maybe, there is no shortcut. Maybe there are no cheats, no loopholes. Maybe we just have to practice patience and accept a degree of uncertainty and doubt.
And, who knows? Patience and the willing acceptance of uncertainty just might be the very spiritual qualities we seek.