I happen to know the author very well - she's not a Christian, but doesn't have anything against the members per se, she just doesn't believe in it.

Also, I don't think she believes in every single thing her characters say. I know the fic in question, and Caitlin's intentionally a deeply flawed character - not evil, but damaged. You're not meant to want to be her or follow her every word. I believe it's called "expecting one's readers to have a brain in their head and use it".