parenting your child effectively doesn't require corporal punishment, so i fail to see how an insane parent that ends up KILLING their child has any bearing on ineffectual parenting.
My point was, it's amazing that any child reaches adulthood with some of the insane parents raising them. What's the line in the movie Parenthood? "You need a license to drive a car, hell, you even need a license to catch a fish, but they'll let any butt reaming asshole be a parent."