Affirmative duties & abortion

Prof. Penlaver (liberal Catholic) responding to Prof. Brennan (quite orthodox) on Prof. Kaveny (kinda liberal Catholic) over at Mirror of Justice

I read her argument as making a narrower point by comparing a woman who carries a child to term at risk to her own health or life to someone who risks his own life to save another. I do not see her actually offering a judgment about whether there is a moral obligation so to act (in either case). The law does not compel a person to act in the latter instance, and the question is why it ought to in the former.

Since all pregnancy involves a degree of risk, Patrick has a point in questioning whether the analogy she makes can be cabined. But I think meaningful distinctions about risk can be drawn here, and I think the analogy is an interesting one. Even if one agrees with the Church's position that a woman is in fact obligated to carry the child to term, does the gap between what is moral and what portion of that category it is wise to try to enforce by law provide room to disagree about whether the state ought to insert itself into a woman's decision in this narrow category of cases?

Am I missing something? True, the law does not impose an affirmative duty to rescue a third party. But it's misleading to suggest that creating a legal prohibition against abortion is analogous to imposing an affirmative duty to rescue the fetus. The current law that says you don't have to save another's life is categorically different from our abortion laws which say not only do we not have to save the fetus' life, but that we have a right to affirmatively and intentionally destroy it. So how is the right to abortion anything like the right to not have to rescue each other? But what do I know? I'm not an Ivy League law professor.