The abortion debate is not really about the lives of fetuses. It never has been. If they really believed that fetuses are human lives, they would only be pursuing one thing: the prosecution of abortions as homicide.
The way the "pro-lifers" actually treat abortion is not as akin to murder at all. They treat it as an action undertaken by people they see as morally reprehensible for other reasons-- the promiscuous, the unwilling mothers. The fetus is not important because it is a human life; it is important because it is seen the natural consequence for promiscuity, for "sinning."
Think about the "moderates" who say that they would allow abortions in cases of rape or where the mother's life is threatened. If the fetus really were a human life, why would the circumstances of the conception (e.g. rape) have any bearing on the fetus' right to life? And why would the health of the mother, either? If the fetus is a live human being, the hippocratic oath binds doctors to keep it alive in the face of a risk to others. But what's important here is that neither the rape victim nor the possible-death-in-childbirth "deserve" the baby as a punishment. Since the rape victim did not consent, she does not deserve punishment at all. And the woman who might die in childbirth may deserve a punishment, but death is too severe.
They instead see the abortion issue as a part of a larger culture war between their way of life and the way of "sin-" homosexuality, sexual liberation, promiscuity, the circumvention of traditional roles for women, and a host of other things. The woman who gets an abortion bothers pro-lifers not so much because she's terminating a fetus, but because she shrugs off what they see as the gravity of her misbehavior by refusing to accept the "consequences."
It all has to do with people "getting what they deserve--" a baby for the promiscuous, death penalty for the murderers, and health care only for those who work for it. In this way, abortion, the death penalty, and private health care all line up perfectly from an ideological perspective. The idea is that if you're an upstanding person, you get taken care of. Otherwise, for many of these conservatives, you're a degenerate and you get what you deserve.
This viewpoint is disgusting and wrong, but when you look at it in this light it is internally consistent.