"Horror . . . takes nothing for granted. It's not safe . . . [It] can be a guide through a nightmare world, entered freely and by the [viewer]'s own will." -- Robert McCammon
“All that we see or seem is but a dream within a dream.” -- Edgar Allan Poe
"There are two different stories in horror: internal and
external. In external horror films, the evil comes from
the outside, the other tribe, this thing in the darkness
that we don't understand. Internal is the human heart."
John Carpenter
Definitions change all the time. Many horror writers reject the marginalization that comes from being labeled a "horror writer." Many film directors also try to break out of the confines of genre.
Politics
Social Status
Ethics and Morals
We fixate on horror because it helps us cope with pain, uncertainty, and fear, while at the same time it subconsciously infects us with morals, ethics, and politics.