Rauch reviews "The Party of Death"

Today's New York Times features this review, by Jonathan Rauch, of Ramesh Ponnuru's book, "The Party of Death."  The review -- critical in places, appreciative in others -- is admirably fair and serious.  Rauch's primary criticism seems to be that Ponnuru refuses to embrace the implications of his own pro-life position: 

“Eight-week-old fetuses do not differ from 10-day-old babies in any way that would justify killing the former,” he writes. “The law will either treat the fetus as a human being with a right to be protected from unjust killing or it will not.” If those are the only choices, and if the right position is that an early-term fetus is a full-fledged person, why not impose jail terms on women who seek abortions? After all, they are taking out a contract for murder. Instead of confronting that question, Ponnuru equivocates, mumbling that “the pro-life movement” does not necessarily seek jail time for women and that fining doctors and revoking medical licenses might suffice.

He believes that discarding or destroying embryos should be forbidden, but should it be punishable as first-degree murder? If not, why not? If an embryo is morally indistinguishable from a newborn, then killing it is surely a heinous crime. If human life is “inviolable,” then why should it matter whether a hopelessly vegetative patient — someone like Terri Schiavo — left instructions not to be fed? Surely, from Ponnuru’s perspective, the doctors caring for her cannot ethically conspire to starve her to death even if she would prefer to die. If every abortion is infanticide, could even the most life-threatening pregnancy be ended? We don’t have a “health exception” to the murder laws.

I'd welcome correction from the moral philosophers who read MOJ, but -- I have to admit -- Rauch's objection here has never seemed as powerful to me as it does to others.  The fact is, our law treats homicides differently, in all kinds of ways.  So, why would a decision not to treat a homicide involving the death of an 8-week-old human fetus exactly like a homicide involving the death of a 36-week-old fetus, or a two-day-old infant, or a 36-year-old woman necessarily reflect the view that the 8-week-old fetus is not actually a "human being"?