He states his basic argument in four steps:
"1. The unborn entity, from the moment of conception, is a full-fledged member of the human community.
"2. It is prima facie morally wrong to kill any member of that community.
"3. Every successful abortion kills an unborn entity, a full-fledged member of the human community.
"4. Therefore, every successful abortion is prima facie morally wrong."
Despite the rigor of his argumentation, I am not fully persuaded because he follows the lead of people like Hadley Arkes and Robert George in adopting a Kantian rationalism that assumes that moral judgment is a matter of pure logic separated from moral emotions. As I have indicated in a previous post, the debate over the moral status of prenatal human life--like all moral debate--cannot be resolved by pure reason alone. Rather, we need a combination of reason and emotion. Thought by itself moves nothing without the motive power of emotion or desire. Normally, we don't feel the same moral concern for a human zygote, embryo, or fetus that we feel for a human infant, child, or adult.
Although Beckwith tries to present his argumentation as a pure logic of morals, he must ultimately appeal implicitly to moral emotions. Thus, for example, his reasoning about "intrinsic value" must assume some "intuition" that depends on moral emotion. For instance, he must assume that his "substance view of persons" conforms to our moral emotions of approbation and disapprobation (p. 140).
And yet he tries to reject "human sentiment" as a basis for moral judgment. He writes: "One usually feels a greater sense of loss at the sudden death of a healthy parent than one feels for the hundreds who die daily of starvation in underdeveloped countries. Does this mean that the latter are less human than one's parent? Certainly not" (p. 153). But surely Beckwith is not saying that it is immoral to feel more concern for one's parents than for strangers (even if one acknowledges their shared humanity). We can feel some concern for suffering strangers, but normally we will feel more concern for those close to us because of the nature of our moral emotions.
Consider also the following passage (pp. 169-170):
"An anonymous reviewer raises an important counterexample to my case: 'Suppose that in an IVF clinic, an earthquake cause (1) a couple of glass dishes to break resulting in ten eggs being accidentally fertilized and (2) a fire in a room in which five patients are trapped. I can either save the fertilized eggs . . . or the patients. Most of us believe that I should save the patients but it is not clear that the sort of substance dualism espoused by the author is compatible with this claim.'
"These types of stories can, of course, always be adjusted to make an entirely different point. For example, suppose the five patients are aging Nazi war criminals and the 10 embryos are one's own offspring. It's pretty clear which group one would save. However, the sort of fictional scenario offered by this referee has been responded to by a number of others. I will offer one reply put forth by Scott B. Rae, who argues that this sort of story confuses epistemology with ontology, that is, it confuses what things appear to us with what things actually are. As Rae writes: 'The surface appearance of an embryo seems too distant and impersonal. But surface appearances and the emotions they engender are, by themselves, inadequate guides for moral reflection. To a lesser degree, this same sort of 'argument' could be used to justify racism, an unjustified preference for individuals who share many of one's own surface features. Since the presence or absence of surface features may be the real basis for the intuitions in this argument, we do not consider it has the force its advocates claim it has.'"
Here we see that both reason and emotion have roles to play in moral judgment. But reason can only elicit the emotions as the ground of moral intuition. So generally we don't feel the same moral concern for human embryos that we feel for human adults, even though intellectually we might be persuaded that the embryos are equally human with the adults. But we might feel more moral concern for 10 embryos that are our own offspring than we would for the 5 Nazi war criminals. Notice that Beckwith must implicitly appeal to our moral emotions. He denigrates the appeal to "surface appearances," but he himself must acknowledge the moral relevance of those "surface appearances."
I have written another post on the related issue of stem-cell research.