I wonder, If you were to make it your mission to confront a part of yourself that is only present in your dreams, something that might be concealed behind the half-consciousness of the dreaming for a very good reason, would you learn something that could disturb you deeply or worse? I do not doubt it; there are dark parts of the mind, and sometimes things need to remain hidden. for example, hypnotic regression is known to uncover things people have often wished had stayed in the dark.
I ask this question after reading about the Jungian archetype of the Shadow; the dark, loathsome, and hidden part of the psyche.
How dark should the dark be in a dream to cause that “hypnotic regression”?
I’ve learnt some things that were meant to be hidden in my dreams and this dark and such things are placebo. The containing of that hidden secrets is not “bad” at all, it’s just the human nature that keeps most from seeing beyond. They are scared about what they are going to find out, so to make sure they will never reveal that secret, they mistify and hide it in darkness.
You said it in your post: things people have often WISHED had stayed in the dark. If there really is such thing like hypnotic regression, it is not determined by what they actually find, but because of the impact of acknowledging something they banned.
In the dreamworld, dark exists only because it covers things people lost or threw away from their RL. I met my shadow(s) and know what? They are not bad and they are not dark at all; they are just blurry and scared by us because [sarcasm]we are much worse and darker than they are[/sarcasm] (this is not the real reason but it fits well here 
).
I found this statement about shadows in your link that, in my opinion, is the best definition for a shadow: “Jung says that if we could fully meet our Shadow, we would be immune to all any moral or verbal insinuations. We would already have seen this for ourselves. Finding this sort of transformation to a state beyond guilt is a task for the hero/ine who has the strength to descend into the underworld and wrestle dark creatures.”
Indeed the shadow is meant to be confronted. When I spoke of hypnotic regression, I was talking about the process by which psychiatrists can hypnotize patients in order to access repressed memories. This has been used in cases of suspected abuse and has uncovered things such as memories of alien abductions (if you believe that). The danger here (if indeed there is any) would stem from the fact that that part of the mind, memories or whathaveyou, would have been shunned by the dreamer, and they may not wish to uncover it. I hate to go back to such dubious situations as alien abductions again but there is a great example, where patients had submitted to the hypnosis due to suspicions of repressed memories of sexual abuse, only to find out they were being abducted by aliens (granted this could be some weird way the mind has of masking the alleged abuse as well.) I fear no danger for myself, but my question rather was about the possibility of such danger, and the shadow archetype just sort of got me thinking about it.