Flannery famously gets a reader to side with a decent but perhaps slightly flawed lady, and then the story slowly turns grim. We see her smile is grounded in pettiness or deep bitterness. Finally, she has a severe encounter with dark grace. Nice readers close the story quickly and refuse to go on to another. It's as if the reader herself has been roughed up unjustly.
But that's the point. Flannery just reflects Christ's priorities. He was much softer on thieves, prostitutes, and murderers than he was on polite, middle class Pharisees. Christ berates and belittles and promises death-from-heaven for the most decent citizens of Jerusalem. The good, law-abiding Rotarian sorts incense Christ's deepest anger. And, in Flannery's stories, grace hunts them down. All evil is not bad. Some evil comes to shake us out of our sin; some evil comes to liberate us. Some evil is a gift of grace. Grace gnashes.