One thing's sure: I've definitely been taking thw wrong approach. I apologize for my part. This thread brought a lot of old resentments up, resentment that the kind of thinking that states "I couldn't kill my kid (I THINK), so they couldn't either" was so prevalent among people who definitely should have known better. And you don't have to take my word for that. I can quote 'em to you.
But enough of that. Perhaps a new perspective is in order. So, I defer to one with far greater wisdom in these matters than I have. FBI behavioral analyst Ron Walker was asked in a TV interview flat-out if he thought a parent were capable of doing this. This is his answer verbatim:
"Well, as much as it pains me to say it, yes. I've seen parents who have decapitated their children, I've seen cases where parents have drowned their children in bathtubs, I've seen cases where parents have strangled their children, have placed them in paper bags and smothered them, have strapped them in car seats and driven them into a body of water, any way that you can think of that a person can kill another person, almost all those ways are also ways that parents can kill their children."