Horror is one of the few genres - romance and comedy are the other two that come to mind - that's all emotion-driven. It's not a rational genre, like science fiction is. It's irrational by nature. And it is capable of exploring all aspects of human experience.
Writing should. . . be as spontaneous and urgent as a letter to a lover, or a message to a friend who has just lost a parent. . . and writing is, in the end, that oddest of anomalies: an intimate letter to a stranger