For all intents and purposes physical evidence points to a brain that is compromised and intoxicated.
There has been a lot of serious research into LSD. The research points to an intoxicated brain just as common sense does.
Imagine there was some alien civilization that chose to transfer some enormous amount of information to you, flooding your senses and completely overwhelming you with information, visions, schematics, sounds, voices, and the emotional impact from having that sort of experience happen to you in a short amount of time.
You would not be fit to drive, because your experience would be completely overwhelming to you, or at the very least you'd be greatly distracted.
That says absolutely nothing about the value of the information you received and whether you should be believed.
Another example: dreams. Clearly you're not fit to drive while dreaming, yet significant discoveries (most famously Kekule's discovery of the ring-structure of beneze) have been inspired by dreams.
Creative, non-scientific output is yet another realm where psychedelic experience has value. You don't have to "believe" a song that someone composed or was inspired to make due to a psychedelic experience for that song to have value. Here [1] is a great example (it starts at about 49 minutes in to the video).
Artwork inspired by psychedelics is incredibly common, and its value is not a matter of belief but of aesthetic appreciation.
"For all intents and purposes physical evidence points to a brain that is compromised and intoxicated."
Compromised or enhanced? Research in psychedelics has clearly shown their healing potential -- quite the opposite of compromising people, they can greatly help them. Enhancing creativity, as mentioned above, is yet another potential benefit. There are many others, such as increasing emotional openness, enhancing empathy, and so on.
You should definitely not drive while on psychedelics.. just as you shouldn't drive while having sex. But it's ridiculous to judge the value of these experiences by whether you can drive safely while having them.
It is quite common for psychedelic experiences to feel "more real than real", and often what has been revealed under their influence can feel like The Truth with a big fat capital T.
I suspect that most people who become true believers after such experiences (and there are a lot of them) are just not very critical thinkers, and don't have a habit of questioning themselves, the world, or what they experience, and so are more liable to swallow the revelations they get line, hook, and sinker without critically diving in to them or coming up with alternate explanations for what might have happened.
Then there are the die-hard atheists and materialists/physicalists, who may be err on the other extreme and hand wave everything they experience as "neurochemical noise" or whatnot. There are a bunch of these also, and when I read their dismissive reports I often wonder how strong their experiences were and how many of them they've had.
Sam Harris, a prominent figure in the so-called "new atheist" movement, actually gave a strong dose of a psychedelic mushroom a try, and reported on his experience.[1]
It's a fascinating account, given by a clearly intelligent and famously critical, anti-religious physicalist which I personally expected to be very negative and glibly dismissive, but to his great credit he treated it very respectfully, seriously, and not dismissively at all.
He did not become a true believer after his trip, but it really made me suspect that if he'd continued taking strong doses of psychedelics even he would have.
Such powerful, convincing experiences are how religious movements start, and no small number of them have started from psychedelics. In fact, some have theorized that many (all?) of the world's great religions ultimately had their roots in psychedelic experiences (see, for example, Allegro's "The Sacred Mushroom and the Cross"[2]).
I hope one day there'll be some serious research in to what is going on here, beyond simply reporting that mystical experiences are common on psychedelics.
[1] - https://www.youtube.com/watch?v=yKGddvmU0fA
[2] - https://en.wikipedia.org/wiki/The_Sacred_Mushroom_and_the_Cr...