A friend made the following argument, and I'm copying and pasting it, here:
Reasonable people can disagree about when a zygote becomes 'human life' - that's a philosophical question. However, regardless of whether or not one believes a fetus is ethically equivalent to an adult, it doesn't obligate a mother to sacrifice her body autonomy for another, innocent or not.
Body autonomy is a critical component of the right to privacy protected by the US Constitution, as decided in Griswold v. Connecticut ( 1965 ) McFall v Shimp (1973), and, of course, Roe v. Wade (1973).
Consider a scenario where you are a perfect bone marrow math for a child with severe aplastic anemia, no other person on earth is a child with severe aplastic anemia, no other person on earth is a close enough match to save the child's life, and the child will certainly die without a bone marrow transplant from you. If you decided that you did not want to donate your marrow to save the child, for whatever reason, the state cannot demand the use of any part of your body without your consent.
It doesn't matter if the procedure required to complete the donation is trivial, or if the rationale for refusing is flimsy and arbitrary, or if the procedure is the only hope the child has to survive, of if the child is a genius or a saint or anything else -- the decision to donate must be voluntary to be constitutional. This right is even extended to a person's body after they die, if they did not voluntarily commit to donate their organs while alive, their organs cannot be harvested after death, regardless of how useless those organs are to the deceased, or how many lives they would save. That's the law.
Use of a woman's uterus to save a life is no different from use of her bone marrow to save a life -- it must be offered voluntarily. By all means. profess your belief that providing one's uterus to save the life is morally just, and refusing it is morally wrong. That is a defensible philosophical position, regardless of who agrees and who disagrees.
But, legally, it must be the woman's choice to carry out the pregnancy. She may
choose to carry the baby to term. She may choose not to. Either decision could be made for all the right reason, all the wrong reasons, or anything in between. But it must be her choice, and protecting the right of body autonomy means the law is on her side. Supporting that precedent is what being pro-choice means.
That I support Roe v Wade means that I reject returning to the days prior to the ruling, because I recall my sister, a young teen, in 1965, who did not tell her parents she was pregnant, who got a unlicensed person to help her abort her child, and she almost died.
I am pro-life because I believe supporting Roe v Wade prevents the deaths and maming of women who will, but for R v W, go underground to get abortions, unsupervised by medical professionals. Moreover, the rich will go to foreign countries because they have the means, so repealing R v W will affect the poor more than the affluent. I suspect there will be a few hypocritical Republicans who will send their teenage daughters to foreign countries to get abortions, should they get impregnated by some young male of whom they do not approve.
Repealing R v W will not stop abortions, but will increase deaths and injuries in women.
You cannot, therefore, argue for 'freedom' and 'pro life' if you do not support body autonomy and the health of women.
You simply cannot.