Humans are pretty smart, obviously, but when you take single human on average they are mediocre at best.(This is by taking into account the widely gaped average "mental performance" as measured by "IQ" etc.) Without a collective effort we wouldn't really be where we are now not only technologically but also socially. Ants obviously topple us when it comes to collective effort but you get the idea of where our "true" intellect is burried.

Now for better or worse, the various psychedelic substances affect the individual brain so much that, depending on the drug, one can go on a totally subjective journey, yet retain objective insights afterwards.

However, I highly doubt that these substances stimulate people to think as rationally, or perhaps scientifically would be a more suitable word if they are not already of that mindset.

The more interesting aspects come from a social perspective, especially mushrooms. As much as I am inclined to think critically, the stoned ape theory just blows my time everytime I think about it. What if, unbeknownst to us, these substances helped us evolve from apes to cavemen? After all, no matter where you look in regards to early civilizations, they all had their fill of crazy substances, whether part of a ritual or not. It's almost as if it's somehow within us to seek out such "rituals" of substance use. Perhaps of the way they affect us in a "tribal" sense? Helps better strengthen the bonds of groups. I'm thinking in circles now, but I hope I shed some interesting perspective.