This could be an immensely long post since the subject is fraught with philosophical land mines, but for me "horror" is fairly straightforward. A story is a horror story solely because its theme is that our world is a veneer over things that are terrible, and that those terrible things will get you. All reprieves in horror stories are temporary.
A horror story is sort of like Norse mythology. In the end the gods die. No one escapes. It's grim stuff, but so is horror.
Many horror stories, it seems to me, are about people discovering this underlying truth. They do their best to escape their fates, and they often do, but they are forever scarred by the experience. Once they know the truth, they'll carry it with them until the end. Some of my favorite horror stories really emphasize the "living with the knowledge" theme, like "Young Goodman Brown," or "The Music of Eric Zahnn." The end of Lord of the Rings, for Frodo, is a kind of horror story. He's too intelligent, and he's seen too much, to be able to go back to the Shire like Sam can (although I wonder if Sam has nightmares).
A weird thing has happened to horror tropes, I've noticed, which is that they've been trivialized. The monster, the vampire, the werewolf have become popular icons. Buffy slays them, but in many stories they are losing their capacity to carry the horror theme. Bram Stoker's Dracula was frightening because most readers hadn't considered the possibility of an undead force actively seeking the most innocent. It was a creepy idea.
Effective horror has to awaken the knowledge in the reader that their world isn't safe. The threat is present and unrelenting.
There are no completely happy endings. The threat may be pushed back, but it's not gone.
A horror story is sort of like Norse mythology. In the end the gods die. No one escapes. It's grim stuff, but so is horror.
Many horror stories, it seems to me, are about people discovering this underlying truth. They do their best to escape their fates, and they often do, but they are forever scarred by the experience. Once they know the truth, they'll carry it with them until the end. Some of my favorite horror stories really emphasize the "living with the knowledge" theme, like "Young Goodman Brown," or "The Music of Eric Zahnn." The end of Lord of the Rings, for Frodo, is a kind of horror story. He's too intelligent, and he's seen too much, to be able to go back to the Shire like Sam can (although I wonder if Sam has nightmares).
A weird thing has happened to horror tropes, I've noticed, which is that they've been trivialized. The monster, the vampire, the werewolf have become popular icons. Buffy slays them, but in many stories they are losing their capacity to carry the horror theme. Bram Stoker's Dracula was frightening because most readers hadn't considered the possibility of an undead force actively seeking the most innocent. It was a creepy idea.
Effective horror has to awaken the knowledge in the reader that their world isn't safe. The threat is present and unrelenting.
There are no completely happy endings. The threat may be pushed back, but it's not gone.
- Current Music:"Na Na, Hey Hey, Kiss Him Goodbye," Steam

Comments
Youngest daughter had a state project due before the school year ended and she got Ohio. Her and her mom made buckeyes and with Top Chef on last night and my sudden discovery that we had about 4 dozen left over in the garage fridge, I couldn't resist.
There also stories of domesticated horror--the enemies of humans get a point of view and social complexities. Humans aren't especially the object of attention. The Anita Blake stories are somewhat in that direction, and I think I can make a case that the Harry Potter novels are a pure example. Wizards are dangerous to muggles, but that's completely glossed over.
Some proper horror still exists, and I recommend "Mr. Brooks", a movie currently in the theaters.
Supernatural horror works on a different level than FATAL VISION, I think. Supernatural horror scares us in a metaphysical way. You're not just going to die: you also exist in a universe that desperately hates you (or could care but doesn't that you exist).
A sudden transformation from the predictable and safe to the chaotic and violently threatening--not unlike how the werewolf was originally presented, no?
My opinions are subject to modification without notice *g*.
It seems to me that Dracula, and a fair amount of what would now be called either horror or dark fantasy published up till around WW I, had a subtext of illicit sex.
And more recent horror has a subtext of illicit use of power.
Still, I get the feeling that Lif and Lifthrasir won't emerge from Ragnarok with a positive religion. And Baldr has too much baggage to rule in Odin's stead. It's not in their nature *g*.
I've got a project that occasionally surfaces, "Cold Gods", dealing with Norse myth from the POVs of Odin and Loki. Probably unsellable, but fun to play with. Rewriting Lokasenna was great fun, and having Odin tell the whole death of Baldr cycle was something I couldn't resist.
I frequently come home from work on Saturday, turn on the Sci Fi channel and laugh at the "science fiction" movies that are little better than comedies to me.
I like your ideas though, and I'll have to quote them some time.
As
I agree with you that true crime is probably the most truly horror-evoking stuff out there. We've turned everything else into a joke or an action/adventure movie. I think part of the problem is the movies mistook suspense for real horror.
The last movie I saw that really terrified me was Outbreak, and the last book that gave me nightmare's was F. Paul Wilson's Night World.
Horror has gone global and we are voting on degrees of EVIL
Of course, it has become a trope in horror movies that the horror is ony temporarily defeated, but that's because of the lure of the sequel..
The dilution typically occurs because repetition of imagery fails to provide a sufficiently distorting theme in the mind of the reader. In consequence, the reader no longer believes that the main character could not possibly accept the premise, so you don't get the catharsis. The first time you see Frankenstein's monster on TV, it's horrific because of what it signifies to you then - false life created from death; the fourth time, it signifies something very different - it's pure parody of life, devoid of metaphysical significance.
Nineteenth and early twentieth century horror went far by converting metaphysical fears into physical fears. The Industrial Age was offering new assurances of physical certainty, and so writers like Shelley, Poe, Lovecraft, Bloch and others sought metaphysical uncertainty and used it as a lever to challenge the emerging assurances.
Nowadays, that doesn't work so well because physical assurances are now too old and well tested. Instead, the new assurances - those we would like to believe but don't fully trust - lie in within ourselves, our beliefs and our relationships. The best horror nowadays is often psychological or sociological - the horror of distorted intimacy (e.g. Misery) and grotesque social adaptation (e.g. Silence of the Lambs). But it still follows the same pattern of a century ago: find the metaphysical uncertainties of the time, and use them to challenge the emerging assurances that we want to trust, but don't quite.
Structurally, I think it's very simple. Thematically, it's fascinating.
I think that's the best definition of horror I've ever seen.