Hi Heisenberg,
I have been researching the question of true, documented side effects to a medium from breaking the instructions or rules of a seance. Other than the warnings you mention, I do not find any compelling literature to support the idea that you shouldn't turn the lights on, grab an apparition, etc. for fear of causing irreparable harm to the medium. Any such references are noted by individual mediums (often cited only on V. Zammitt's site), mostly it appears to let them run the illusions/effects without question.
Helen Duncan, for example did not die until weeks after the seance was interrupted by the police, and was said by an examining doctor on the scene to have "advanced diabetes and heart disease." I'm sure the shock of being raided by the police didn't help matters, but please.... What she was doing bound in a "spirit cabinet," (a common parlor trick device of the late 1800s)? - well it boggles the mind, as it was never a requirement for mediums and was adopted from the illusionists of the day.
Thompson's seances were reportedly rife with common or accomplished parlor tricks as well. He would have himself bound, then draped behind a curtain, and certain thoroughly debunked items such as a spirit horn (which Houdini and others investigated reproduced the effect and disproved) would appear to fly around the room. After his materializations, the curtain would be opened and it would be shown that he was still bound. Bravo. But, I mean come on, really. This is a stage show not an ADC.
I don't distinguish between physical mediumship and mental or psychic contact, because each case should be afterlife contact either way. I have seen myself that discarnate spirits begin to lose their association with the physical world in the second stage of death. It is a matter as Swedenborg notes of correspondences; without physical equivalents in the realm of mind/spirit, certain earth associations and knowledge simply fade away.
The spirit horn, the whilrling levitating table, spirit writing slates were all used by the so called physical mediums, mostly since the age of spiritualism and illusionists. I don't believe just any common person will always know recognize or know the illusions employed (this was true of Houidini's stage tricks as well). The reason I am so strongly anti-"dog and pony show" mediumship is that I am so certain that it is, for the most part a sham.
I maintain that to contact the other side, with any real contact (physical or mental) there is no known logical reason that a show must be put on behind a curtain, and no compelling reason to allow the mediums to dictate the terms for our examination. As you said either the contact is real or out and out fraud. The problem is, if you accept the preconditions of the illusionists/mediums, then you prevent yourself from using your own tools of discernment.
Illusionists have done amazing things. David Copperfield made the statue of Liberty seem to disappear on live television. Video of it is still available on youtube. Yet it was a spectacular illusion. There were thousands present on stage with him; most if not all present would have sworn to the fact that the towering statue dematerialized. Yet Copperfield is an illusionist, and we know it was a clever trick (likely done with the audience sitting on the equivalent of a massive turntable which moved them rather than the statue).
The Seybert report and Houdini's texts go into detail as to how most common physical medium tricks appear to work.
But perhaps the greatest source (also available online is the modern book by a confessed physical medium named Lamar Keene called "The Psychic Mafia," in which he describes, in detail how he performed all the parlor tricks described with spirit horns and the like - and how the medium community he was part of knew all about it:
http://members.fortunecity.com/misteryo/pm1.htmlWe all need to use our own powers of discernment here, but most of all, we should continue to explore on our own, in different ways - always mindful that our own explorations are usually the path to discovery.
Matthew