How to understand a woman's obligations to the fetus in unwanted pregnancies

Some have challenged Thomson's case of the famous unconscious violinist (UV) by arguing that in cases of consensual sex a woman is partially morally responsible for the existence of a needy fetus; since she is partially responsible she ought to assist the fetus, and so abortion is morally wrong. Call this the Responsibility Objection (RO) to UV. In this paper, I briefly criticize one of the most widely discussed objections to RO and then suggest a new way to challenge RO. In so doing, I investigate the plausibility of the moral principle that appears to be driving RO: If a woman is partially morally responsible for the existence of a needy fetus, she has a moral obligation to assist the fetus. I argue that this principle is false. I suggest modified versions of this principle but argue that, even on the most plausible version, RO does not persuade.