Their gotcha Catholic argument is this: Augustine and Thomas, dominant figures in the development of Catholic theology, held that humanization did not occur until after conception. Dombrowski and Deltete think this notion of delayed humanization should be determinative for Catholic teaching, even though Augustine and Thomas did not conclude, as the authors do, that delayed humanization makes abortion permissible. The authors believe that the Catholic Church's teaching rests mistakenly on a sixteenth century scientific notion that the sperm contained a fully formed human being (a homunculus). This perfectly formed miniature body contained a soul; hence a human person was present. The authors argue that the authority of Thomas and Augustine on delayed humanization ought to trump bad science. Were that all there was to the argument, they might have a point.
But that is not all. Catholics do not consider that a human person is present from the moment of conception. Even so, the human life that is present has moral standing such that it should not be aborted. Though the authors want to devise a "liberal" Catholic argument, they deplore the fact that even the most liberal Catholic philosophers and theologians (Richard McCormick, Thomas Shannon, and Lisa Sowle Cahill) are unwilling to press the church's prohibition beyond implantation in the uterus at about one week. At that time, the chance of twinning has ended, and an individual human life is present, one that has moral standing deserving of respect and protection. That is about as far as many liberal Catholics will go. But it is far short of the line that Dombrowski and Deltete draw.
As a liberal Catholic myself, I find the two singularly unpersuasive on a number of points. Let me mention two. One hallmark of liberal Catholicism is to hold that church teaching must acknowledge the "development of doctrine." They never mention the idea or its criteria. Is that because the outcome in this case is likely to depart from theirs? Thus while they appropriate the views on fetal development of Thomas and Augustine, who knew virtually nothing about reproductive biology, they reject their views on abortion. Development of doctrine depends not only on new (and forgotten) theological and philosophical insights, but also on new scientific information. Today's genetics show that a new human life is actually created at conception. Does this count for nothing? Not for the authors who insist that full moral standing comes only with a fully developed cerebral cortex. Where does that leave humans with defective (the retarded), diminished (the elderly), or damaged (accident victims) cerebral cortexes. Do they lose moral standing as human persons? I doubt these philosophers would want to draw that conclusion.
They might argue, however, that the fetus is different, that the significant early wastage of fertilized eggs shows that God (or nature) does not hold fetal life to be morally significant. But I ask: Once implantation takes place, shouldn't a developing human life be treated as if it were likely to become a human person? (In fact, given the wastage rate, perhaps we should be even more careful of those fetuses that survive this early winnowing process.) The authors might counter-argue by asking: Should this human life, which is only potentially a human, trump a woman's right to an abortion? The moral intuition of many Americans, reflected in opinion polls, is: that depends--on when and why. Abortion early in a pregnancy--say the first two months--is less morally problematic than one later; that grave reasons (to save a mother's life) may justify a later abortion, but that justifications for social, economic, or convenience reasons do not. Given that Dombrowski and Deltete would seem to sanction abortions well into the third trimester, aren't the moral intuitions of most Americans closer to the views of the Catholic Church than to theirs? If so, the consensus the authors spend a chapter promoting would seem to be a consensus that both Catholics and others would reject.
This leads to the second problem I have with their argument. They avoid entirely a central moral question of the abortion debate. What counts as a justifiable reason for abortion? Can abortion-on-demand through twenty-four weeks for any reason whatsoever be justified? The Supreme Court says yes. As I have noted, most Americans don't agree with the Court. Who then will agree with Dombrowski and Deltete who are even more expansive; by their reckoning abortions could be permissible through the sixth or seventh month of pregnancy. Perhaps in their eagerness to draw a firm philosophical line, they fail to confront the human problem of where they have drawn it. One of the most dramatic objections would be the live birth of an infant who would look very much like a human being, although by their criteria it is not a human person. What then is it? Back to the philosophical drawing board, guys.