Bold hypothesis time. Psychedelics are not like other mind altering substances. It is not a general blunting such as drinking nor a general heightening such as a stimulant. Rather, it seems to interfere in a particular band of brainwave activity. The bands of brainwaves work much like TV channels, a priori they are just a medium for whatever content without particular purpose or semantics. Much the same way the sports channel in one country might be the news channel in another, different brains will allocate their frequency space in slightly different ways. This is why some people get "the giggles" on acid, some people get disturbing "bad trips", and some people just get cool visuals but are otherwise fine. In all cases, its the same frequencies being distorted, but the thing each individual brain is coding on those channels differs.
Can psychedelics cure depression? Depends, what frequency band of brain wave is your brain using for emotional state?