There are very few cases of an abortion is necessary to save the life of the mother (in which case, her consent is irrelevant). The halachic approach is that this is still homicide, but it is justifiable homicide (for the same reason that it is lawful to kill someone who is threatening your life). Very few pro-lifers opposed abortions when the issue is saving the mother’s life.
Once you say it is a parent’s right to kill their kid, you then get into questions such as “is it their duty” if the child is defective, what if the child is merely inferior, what about adults who being old and disabled have no potential for further accomplishments and are just “eaters” rather than producers, what about groups of persons who accomplish little in life but consume many resources and may in fact be a burden due to low productivity and high criminality …. (and thus you have the pro-life argument that legalized abortion puts you on the road to gas chambers and ethnic cleansing).