I just re-read a different story by the same author ("Everything That Rises Must Converge"), because I mentioned Flannery O' Conner in another thread. She tended to write dark. "A Good Man is Hard to Find" was the one about the family on vacation that encounters a serial killer, right? It's been many years since I read it, but if I remember correctly, "A Good Man is Hard to Find" was deconstructing the basic "Feel Good" approach to storytelling, where decency and an appeal to someone's better nature overcomes any adversity and narrative justice is served. I also remember that the family in question was rather unpleasant. She was good at portraying unpleasant protagonists faced with even more unpleasant circumstances.
She was a devout Catholic living in the mostly-fundamentalist Protestant South. As I understand it, this had a huge effect on her world view. She died very young, at 39 (in the early 60s). I can't help wondering how her writing and philosophy might have evolved if she'd lived a fuller lifespan.
I've often wondered if the person who originally penned the story that was the nucleus for the movie Vacation (it was originally a short in National Lampoon Magazine) had read this story back in school or something. Though the National Lampoon version was much cruder and was obviously aimed at anti-social teenaged boys.