That's because he didn't write, nor intend to write, a horrible terrible disturbed woman beyond redemption. The genesis of Carrie (told in its entirety in the 1999 edition's introduction that you can read here, and in King's memoir On Writing), was this: sometime in high school, King read an article in Life magazine about supposed poltergeist activity in a home, which seemed to be associated with the teenage girl who lived there. The article included the hypothesis that poltergeist activity is, in some way, tapped into or manifested by girls at that critical and tumultuous age.
And some years before that, King had gone to school with a couple of girls he pseudonymously calls Tina and Sandra, who were bullied and shunned by the other kids—Tina for wearing the same clothes every day, Sandra for her epilepsy and extremely religious mother, but both really for having some undefinable Other quality that kids pick up on like blood in the water. Both of them were dead by the time King began writing Carrie: Tina by suicide, Sandra from her epilepsy.
Carrie was what King imagined might have happened if that explanation of poltergeist activity were correct, and if Tina and Sandra had been able to tap into such an energy. He started writing the story a few years after getting married (his wife Tabitha is also a writer), but abandoned the idea a few pages in; the raw, merciless adolescent cruelty the story called for was too much to deal with, and what did he know about teenage girls, anyway? But Tabitha dug the pages out of the trash and read them, and convinced him it was a story that needed telling.
Carrie is a story which, perhaps like poltergeist activity, could only happen to a girl on the brink of womanhood, when every emotion and sensation is excruciatingly vivid and nothing makes sense anymore and every single occurrence in your life is the most important thing that will ever happen to you. It's about being horribly powerful and vulnerable at the same time, and alienated from your own body. It's about the visceral, starved animal fear and rage of being a teenage girl, and it goes to show what an arcane and powerful craft creative writing is that a man could manage to capture that without having experienced it firsthand.
"Sometimes—quite often, in fact—I wish that Tina and Sandy were alive to read it," King says in the 1999 introduction to Carrie. "Or their daughters."
