"It was the seventh deadly sin. My children weren't righteous. They stumbled because I was evil. The way I was raising them they could never be saved. ... Better for someone else to tie a millstone around their neck and cast them in a river than stumble. They were going to perish."
Certainly there's crazy in everybody who kills people, but there's something perversely noble about sacrificing everything you have in this life, for your children's next life. If you believe yourself damned and all you have is to spend the rest of your life before burning forever in Hell. And your kids are going to stray and you can spare them from your fate. You can trade the rest of your life on Earth before you burn forever in hell, in order to send your children straight to Heaven. Ask any contemporary Christian (as non-contemporary ones believe in infant damnation) where Andrea Yates children are and they will say Heaven. -- If you buy into that worldview, didn't Andrea Yates really give up everything she had for the good of her children?
The truth is she was crazy, believed in this religion stuff, suffering from postpartum depression and murdered her children. But, from the Christian worldview she should be a martyr!