Why not just say, "that sounds like something Hitler would say?". It shows you are debating with someone that has no interest in debating.
That's the entire point - that the language used to dehumanize a fetus has a similarity to the langauge used to dehumanize an ethnic group - and both have been a precursor to mass murder, with 30 million dead in the United States from abortion and millions dead from genocide around the world. Nat Hentoff, a principled liberal, is wise enough to recogize that slipperly slope and not condone the first step out onto said slope.
If you wish to make a religious argument against abortion, fine. I wish to make a secular argument that takes away the refuge of those who try to downplay opposition to abortion as the realm of religious fanatics - by using their own concepts of human rights against their justifications for abortion.