Even animals only do it rarely.
When animals do kill their offspring it is when the newborn is sick or unlikely to survive. There are cases where a newly born or aborted infant is so compromised that it will not survive and is physically grotesque. The parents and doctors may decide that it is useless to try to preserve life. The parents may refuse the infant, and/or have no way to pay for a lifetime of hospital or constant home care. The hospitals would go out of business if they were left caring for every helpless infant who will continue to need constant care until they die. I don’t believe the Trump medical bill made provisions for such issues. Therefore your tax dollars would pay for the constant care of an ever increasing number of the hopeless and deformed. Years ago I went to a mental hospital as part of a sociology class. There I saw a 23 year old bearded shrunken deformed man in the fetal position sucking his thumb in a crib. He was unable to roll over, sit up or do anything else a one year old infant could do. I also saw several children who were around 4 or 5 and deaf and blind. They were sitting on the ground, not moving or reacting to anything, and receiving nothing but feeding and cleaning. I also shared a group therapy situation with a young woman whose child had died of Tay-Sacks (sp?) Disease, a heredity condition which leads to early death. She had spent 4 years caring for this child until it died as predicted. She was now pregnant again and planning on getting an amniocentices genetic test of the fetus. She then would face an abortion or no abortion decision. These are the situations that doctors and parents face when at late term a serious medical condition is discovered.