For me, I believe that the bond is very natural, almost instinctual. I can't fathom how a woman can give birth to someone and not love it and die protecting it. Still, I see it happen over and over again. It seems to me that a lot of women do it out of mental illness or because of or for a man. Remember Susan Smith? Obviously there was something wrong with her, but she drowned her two boys because the man she was seeing didn't want to be tied down to a woman with children. They were an inconvenience to her and something she needed to get rid of. Then you look at Andrea Yates and she was someone who was completely mentally ill and not prepared to handle those children.
Whatever it is, bond or not, it's just sad to me.