If it is the uniqueness of human embryos that makes it wrong to destroy them, then there is no compelling reason not to take one cell from an embryo and destroy the remainder of it to obtain stem cells, for the embryo's unique genetic potential would be preserved.Much has been made about the fetishization of potentiality over and against actual postpartum life in the pro-life movement. And there's some truth to that pro-choice argument. But neither potentiality nor genetic uniqueness is by any stretch a cornerstone of a Catholic defense of the dignity of the fetus. What has underwritten Singer's position and what will make it so compelling for many today is the loss of a classical metaphysical understanding of quiddity and formal cause. This is where Cardinal Schoenborn's recent First Things article against Neo-Darwinism is very germane. Singer has to split hairs and build strawmen out of them in order to make this nonsequitur argument which has the logical relevance of Monty Python's "Every Sperm is Sacred."
This possibility highlights the weakness of the argument that abortion, too, is wrong because it destroys a genetically unique human being. By this reasoning, a woman who finds herself pregnant at an inconvenient time could have an abortion, as long as she preserves a single cell from the fetus to ensure that its unique genetic potential is preserved.
But it seems absurd that this should make any difference to the morality of aborting the fetus. If, at a later date, the woman wants to have a child, why should she use the DNA of her earlier, aborted fetus rather than conceiving another fetus in the usual way?
Each fetus - the one she aborts and the one she later conceives through sexual intercourse - has its own unique DNA. In the absence of special reasons, such as a change in sexual partners, there seems to be no reason to prefer the existence of one child to that of the other.
Perhaps the assumption is that, as opponents of abortion sometimes say, the aborted fetus had the genetic potential to become a Beethoven or an Einstein. But, for all we know, it is the next fetus that the woman will conceive, not the one she aborted, that will turn out to be the Beethoven or Einstein. So why prefer one genetic potential over the other?
Once we abandon arguments based on potential, the claim that it is wrong to kill embryos and fetuses must be based on the nature of those entities themselves: that they are actual human beings who already possess the characteristics that make killing wrong.
But because fetuses, at least at the stage of development when most abortions are performed, have yet to develop any kind of consciousness, it seems reasonable to regard ending their lives as much less serious than killing a normal human being. If so, then this is all the more true of embryos.
Catholics care about what things are, the "Ding an sich" to which Kantianism wrongly denied us epistemological access. Call it what you want, but a human fertilized egg, even a cloned one, is a human being in the full context of its biology and its natural telos. But it doesn't end there. The Catholic pro-life position is careful to distinguish between what nature does and what we freely do with our moral agency. The quiddity of Hwang's experiments is the intentional and artificial creation of human life by moral indifference towards that life and for the willful purpose of destroying it. That crosses moral lines all over the place, and that's where Catholics object. Singer's piece is off in lalaland if he thinks his rationale even comes close to the Catholic pro-life position.