The responsible and moral thing to do in such situations is to attempt to save both patients while not attempting to kill either.
The "for the life of the mother" justification is totally specious. If your wife and I were being held at gunpoint by a murderer, and he said that either we will both die at his hands, or I can shoot your wife and he will spare me, could I legally and morally shoot your wife to save my own skin?
Obviously not.
So why do so many think its just fine for a mother to kill her child to save her own neck?
That certainly is the most desireable situation, but sadly, it frequently not the case. An Ob-Gyn needs to know how to performan abortion because situations will arise where it is necessary to save the life of the mother. By having a blanket 'no abortion at any time or any circumstance' is cruel and foolish. It would condemn women to death.