Edward Abbey once said, "Abolition of a woman's right to abortion, when and if she wants it, amounts to compulsory maternity: a form of rape by the state."
I would respond with a question: "By prohibiting women from killing their newborn babies, is the state forcing women to be mothers -- compulsory maternity?"
Almost everyone would say no. After all, a woman with a newborn baby is already a mother. And clearly she may not kill her son or daughter -- an innocent human person -- simply because he or she is in the way and needs to be cared for. That's called murder.
Abbey would probably say that abortion (killing the unborn) is much different than killing an infant. And that's the real issue: whether or not abortion is the killing of a valuable person, like an infant. If it's not, then I agree with Abbey that it makes little sense for the government to prevent a woman from having an abortion.
But if abortion does kill a human person, then a pregnant woman already is a mother, and it makes no more sense to permit her to have her unborn child killed than it does to permit infanticide.