snowberryZ
That's not how I read it.
My mother was never very maternal and the three of us didn't turn into cruel children and mass murderers.
In the film the mother was constantly rejected by Kevin.
He was unlovable
I think it was more nature than nurture.
He was a bad apple.
Other than the one time she snapped, (after being continually mentally tortured by him) she never showed cruelty to him.
It's strange how we all take different things from it.
Indeed, and that's a sign of a good book, I think. The nature/nurture argument was left open for the reader to decide.
In the film we saw everything through the mother's eyes, and it was clear that even as a baby she thought Kevin was deliberately acting to spite her, which is impossible, whereas the book definitely suggested that there was another side to every incident. She thought that his delayed speech was deliberate, and that he was being uncooperative when he couldn't play the games she wanted him to.
I can't remember in detail now, but wasn't there a time when Kevin was blamed for throwing bricks off a road bridge, and it turned out not to be him at all? There was doubt about the guinea pig/hamster incident, too - in fact he wasn't definitely guilty of anything except disrupting her life - and she was entirely unable to warn to him, or relate in any way. I would say she was mentally cruel from the day he was born.
As you say, though, it's not certain - I think that Lionel Shriver said that she didn't know the answer either - she just wanted to write about what might happen if a mother didn't love her child.