Is it consistent to support both fetal rights and the moral acceptability of capital punishment? That depends on what is meant by 'consistent.' Let us begin by asking whether the following propositions are logically consistent.
P1. A living human fetus has a right to life which cannot be overridden except in rare cases (e.g. threat to the life of the mother).
P2. Capital punishment for certain offences is morally justified.
The question, then, is whether (P1) and (P2) are logically consistent. To say that two propositions are logically consistent is to say that they can both be true. To say that two propositions are logically inconsistent is to say that they cannot both be true. To show that two propositions are logically consistent it is not necessary to show that they are true; it suffices to show that it is possible that they be true. Thus, BV is a world class runner is logically consistent with BV is a world class mountain biker even though both propositions are (spectacularly!) false.
Now are (P1) and (P2) logically consistent in the sense lately defined? Obviously they are. Suppose that the right to life is grounded in the potentiality to develop into something to which one accords person-status, where a person is a rights-possessor. This is a possible view, and indeed one actually held by many. Any Aristotelian worth his salt will be able to spell it out coherently and perhaps even persuasively. Suppose also that a similarly coherent case is made for (P2). One will then have made a case for the possibility of their both being true. So why should anyone think that (P1) and (P2) are inconsistent? On the face of it, they are logically consistent.
So why do so many people think they are inconsistent? Perhaps these people are not concerned with the question of logical consistency, which is a relation between or among propositions. Perhaps they are thinking in terms of consistency in the application of a principle. Consistency in this sense is not a relation between or among propositions, but involves a person who applies a principle to cases that it may or may not subsume. The first type of consistency is purely logical; the second is pragmatic.
To apply a principle consistently is to apply it to all like cases in a like manner. So if the principle is to cherish, value, uphold human life, then perhaps their thought is that to apply this principle to the unborn but not to certain criminals is to apply it inconsistently. "How can you oppose the killing of the unborn, when you favor the killing of certain criminals? Be consistent!"
The answer to this should be obvious. The cases are dissimilar. The unborn are all of them innocent while criminals in general are not. This is a difference that makes a moral difference; it is a difference that justifies a difference in treatment. No doubt principles should be applied to like cases in a like manner. But there is no inconsistency in refusing to apply a principle to cases that are relevantly dissimilar.
One who is 'pro-life' need not hold the absurd view that in no circumstances may human life be taken. For surely there are circumstances in which it is morally permissible, and perhaps even morally obligatory, to take human life. Self-defense is one case, just war is another, and capital punishment is a third. Indeed, it precisely because one is pro-life that one will defend oneself and others from murderers using means up to and including the talking of their lives!
This is all so obvious that I am astonished that people routinely repeat the charge that it is inconsistent to support both a right to life for the unborn and the death penalty. Where is the inconsistency? There is no logical inconsistency and there is no inconsistency in the application of a principle.