What is more "dark", a psychedelic mostly devoid of emotion making it feel more cold and serious, or just neutral (2C-E, 2C-D, 25D for me - I can certainly imagine what people mean when they talk about DOM) or psychedelics that are strongly emotional like mushrooms for me, in which case the emotions can run very positive and high or very negative and low? And the whole rich spectrum in between of course.
It depends on how you look at it I guess.
But I also agree with sentiments about DPT. It's less neutral and transparent like 2C-E is IMO, but like 2C-E there is such a strong and profound sense of a majestic mysticism that I suppose you can call dark in that it can become frighteningly overwhelming without compensating with an embracing comfort like one is likely to get on say DMT. Then again I don't mean to say that DPT cannot be comforting and supportive in any other person or that DMT could never be brutal.
I've heard about DOI being called evil and my experiences with DOB did in a way reflect an overly rational and subjectively inhuman mental potency...
Other than all this "dark" is just an adjective that shows how we project our own emotions as a part of the psychedelia we seek. If a psychedelic is very good at its job and there is the right mix of ball-gripping immersion or derealization combined with a number of other such striking effects I guess we may be more likely to attribute a darkness in the drug's character. But in the end we only get an amplified version of what we put in don't we? Unless there is an increased propensity for dysphoria as with salvia.
If not, I think we can consider the ways in which a psychedelic demonstrates the good and the bad, for example the visions of, I quote, 'gwar-style death' mentioned in
this DOC report. Indeed the amphetamine / dopaminergic component of DOX compounds may make any negatively charged images more manic. But on the other hand if the images are positive we can expect them to be seen as equally fantastic just differently charged.
What I mean to impress is that unless there is an intrinsic dysphoria it may not be fair to call certain psychedelics dark. Although a very high potency may increase the odds of becoming overwhelmed and slipping into a state of bewildered fear.