I believe that all profound human fears, phobias, and taboos have a specific genetic or cultural origin. You can be as Freudian as you wanna be, but I believe that humans fear snakes because natural selection dealt with those who didn't. Same goes with flying. I'm terrified of flying, and it's not because I fear a "loss of control." It's because my ancestors who didn't fear it were otherwise prevented from contributing to my gene pool.
But what about fears that have no apparent rational basis? Most cultures have a profound (but largely unconscious) fear of "ghosts," and most cultures, past and present, have strong taboos against contacting the deceased. Since science largely insists that ghosts don't exist, and that it's impossible to communicate with the spirit world, what is the origin of these aversions?
These are the working hypotheses that I began to tossing around as I have begun reading Joe Fisher's "Hungry Ghosts." In fact, I did not have to finish the first chapter without having a small epiphany: That if you attempt to initiate open-ended communication with the spirit world, with no preconditions or safeguards, you're liable to bring down some serious trouble.
I believe that our ancestors learned directly not to do this. And although these specific unpleasant experiences have disappeared from our collective memory, the terrors spawned by these early spirit explorations persist in most living cultures.
So, societies created specific rituals and safeguards that regulated human-spirit communication. The ancients learned that before one intrudes into the spirit (or near astral) realm, consciousness must be modulated and focussed through prayer, ritual, and meditation; intent should be specific and positive; and there should be an interceder (physical or otherwise) to serve as an added buffer.
Our ancestors understood that in the spirit realm, unconscious terror becomes objectified monsters... Our slightest thoughts are instantly materialized... And most importantly, we will attract only those spirits that are "like us"--morally, ethically, and otherwise.
On a side note, I'm re-reading "The Key." I think that I last read it pre-9/11, or shortly thereafter. I'm one of the few people that ponied up the $20 or whatnot to get the first edition. I well remember how it unsettled and disturbed me then.