I have an ethical reason for this. It's easy for us to say that a mother shouldn't do one cruel act that we consider immoral. But we just shrug off the years of abuse and neglect that result from a mother not loving her child because they aren't as fantastically immoral or noticeable.
A woman gets pregnant because she was careless, but has no desire to have a baby. She's prevented from getting the abortion, and the baby is born.
For eighteen years, that baby is treated by the mother like a zit she couldn't get rid of. If it isn't subjected to physical and emotional abuse, it certainly isn't given love or support. It grows up lacking any bond with the parents, and suffers for years because of that. It has behavioral problems, emotional development problems, and resorts to either extreme acts in order to get attention or implodes completely and shuts itself off.
I'm sure we could find an example of someone defying those odds and finding happiness in life. That does shit all for the countless number of children who don't defy the odds and either commit suicide, end up in prison, end up addicted to drugs, end up uneducated, etc. before it manages to build its own support structure.
If a mother is callous enough to want to kill her baby, I'd rather she do it while it's unconscious than it have to live with a woman like that for a lifetime of conscious awareness that it isn't loved or wanted. She shouldn't be stopped because we care about the baby while it's cute. I've yet to see a single case of us caring about the baby after it's born and us providing the happy life we supposedly kept it from being denied. We don't care enough about it to give it the eighteen years it deserves, we only care about it for eight months. That's not a valid reason to subject a child to a living hell.