The topic: "Books that, if read, represent a threat to your sanity."
Well, sure. ANY book, depending on who and what you are, represents a threat to your sanity; it simply depends on who and what you are. In real life, I once knew a kid who, through careful study of the Bible, concluded that music was evil, and that the more music you listened to -- whether you wanted to or not -- the more threat to your soul of going to Hell.
We couldn't let him in the day room in the rest home; if the TV was on, well, you know that every commercial has its own jingle, and he'd attack the TV set.
Consequently, it could be said that the Bible drove this poor kid insane. Interestingly, he would not be the first; people who develop psychoses often latch onto something in the Bible as justification for it. Does this mean that the Bible was responsible for their insanity?
Yes and no. Most people who read the Bible are not insane (although after watching certain revival shows on Sunday morning, some could make a case otherwise). In real life, usually, the person starts out nuts in some way -- his reading material is usually just nightmare fuel that points him in a certain direction, or provides a justification for some craziness he's already decided on. My Bible-thumping kid patient, above, is an example of the latter (since I'm quite sure it doesn't say a durn thing in the Bible about music being evil).
So... can a book, or piece of knowledge, drive you crazy? Perhaps. Depends on how firm your grip on your sanity was to begin with, or the nature of the information. If I were to discover that my late mother had been Jewish, this information would impact my mind and life... not at all. I couldn't care less.
If I were Hitler, on the other hand, or an Islamic bomb zealot, this might have been a pretty big thing, don'cha think? Strong enough to rattle my cage, maybe? Shake a few nuts and bolts loose?
One of writer H.P. Lovecraft's favorite tropes in his fiction involved the idea of "Shattering Epiphany," that is to say, "a character learns an essential truth of the universe... and can't handle it, and goes stark raving fruity-gumballs, right there on the spot." In short, Mom wasn't Jewish, she was a hideous slime alien from the constellation of Paisley IV, and her DNA is starting to wake up in my own cells, right this minute...
Often, these "essential truths" are found in books. His famous Necronomicon is a prime example of this. The hideous play The King In Yellow is another. Others included the evil witch-book De Vermiis Mysteriis, the Revelations of Glaaki (ten spiral notebooks written during the Sixties by an insane hippie), the secret history of Earth contained in The Pnakotic Manuscripts and the Eltdown Shards, the pre-human mysteries of the Scrolls of Skelos... Lovecraft and his buds left us quite a library of books you don't dare read; I've barely scratched the surface. Other authors have added on; one author whose name I can't remember added on the hideous Massa Requiem de Shuggay, a full-length opera which if performed correctly causes the Apocalypse to happen partway through the third act, and Le Fin Absolue de Monde (The Absolute End Of The World), a film which, if watched, will drive the watcher to act on his darkest or most painful impulses... unleashing his inner demons, so to speak.
...so here's the question: WHY would anyone create such a work?
In fiction, there are lots of reasons. The Necronomicon, the Pnakotic Manuscripts, and the Eltdown Shards were written by scholars to preserve knowledge. Only afterwards did it become obvious that some people simply couldn't handle the knowledge in question. The Necronomicon's author, Abdul Alhazred, did not go insane, although he did suffer some pretty bad nights. However, he did wind up getting torn apart by invisible demons who didn't much care for the publication of their names and addresses. We can classify works like this as "Mostly Safe, if you have the mental strength to handle the truth."
Le Fin Absolue de Monde was created by a film director in the name of extreme art. He didn't realize how powerfully he'd succeeded until his own creation drove him insane. We can classify this as "Mind Poison, Unsafe At Any Speed."
No one knows who wrote The King In Yellow, so no reason can be given for its creation. However, it is highly unlikely that the play has ever actually been performed; in Robert Chambers' stories, the people who come in contact with it merely read the play.
Le Massa Requiem de Shuggay was written by a mad Italian operatist who thought that it was high time for the Apocalypse, and used his musical genius to craft an opera which acted as a summoning spell for the mad demon-god Azathoth; since Azathoth is the size of a galaxy all by himself, summoning him into a Milan opera house would have the same effect on our planet as a sledgehammer would have on a hummingbird egg. Overkill? Sure. But the author was crazy, remember. Classification? "Atomic Bomb"
De Vermiis Mysteriis, the Mysteries of the Worm, and the Revelations of Glaaki share a classification. In the story of the first, we find Ludvig Prinn, a medieval wizard imprisoned for his blasphemous sorceries, who wrote De Vermiis Mysteriis in prison. Our protagonists obtain a copy and use it to gain eldritch knowledge... only to discover too late that Prinn wrote the book as an act of revenge: it contains any number of summoning spells to unleash primal alien horrors into the world... but the spells for containing them and sending them back are mere gibberish, powerless. In the second, we find that the crazy lakeside hippie who wrote the Revelations was a mind-puppet of the alien Glaaki, who was unable to leave the lake... but wanted people to read the notebooks and use them to accidentally summon horror-servitors that COULD walk the earth freely.... Classification: "Gateway For Nightmares."
The Scrolls of Skelos were a series of spellbooks and research notes compiled by the reptile race that ruled the earth right before humanity arose and claimed dominance (in the King Kull and Conan stories of Robert E. Howard). They are decipherable... but created by alien minds, and were never intended for use by human sorcerers or human minds. They were easy to misunderstand or misuse (human mouths were not designed to correctly pronounce the serpent people's magic words), and it was easy enough to unleash something dangerous to body, mind, or soul. Classification? "Alien Weapon, Handle With Care, Engage Safety Before Use."
So, Hobbes, if you're reading this.... which do you think it is?