Freddie has a characteristically anguished (and honest) post about abortion up at the League of Ordinary Gentlemen. He writes that the arc of American liberalism is to extend human rights to ever broader groups of individuals. I think he’s right, and whether that arc is a good one or not, American liberals — good old-fashioned big-D Democrats — ought to be pro-life. Of course, the problem with giving fetuses a right to life is that you are diminishing the autonomy of women. This is why abortion is such a torturous issue, or should be, for liberals. Broadening human rights and maximizing autonomy are both cherished liberal ideals, and in the case of abortion there really is a zero-sum conflict between them.
One of his commenters makes an often heard but false claim:
It is worth pointing out, in such discussions, that if humanness (in the mere biological sense) is sufficient for rights, then every single cell in a human body has such rights — including malignant cancer cells.
It should be clear that something different is meant when you call a person “human” and when you call a human skin cell “human” even without delving into the unpleasant details about the set properties of the predicate. You can say of a newly fertilized egg, for instance, that it has a particular mother and father and a particular predisposition to develop Alzheimer’s. In short, it is a human, a member of the human species. While skin cells are “human” in some sense, they are not in any sense members of the human species. Being a human being does not necessarily mean you get human rights, of course — perhaps you can be a human being but not a person, which is what pro-choicers generally say about embryos and fetuses — but any particular human cell is not a human, as an embryo is.