Short answer: Yes.

However, the reason why is not so simple. I found an answer by Germain Grisez which, it seems to me, is satisfactory:

I am a woman, a nurse, and consider myself a feminist, but I accept the Church’s teaching that abortion is always wrong. Indeed, if the Church did not teach that, I would have a hard time believing anything it does teach about practical matters. I also am convinced that abortion should no more be legal than killing you or me or anyone else. But the fact of the matter is that in this country abortion is legal and, at least for now, there does not seem much hope of making it illegal. We therefore need some clear guidelines on our duties regarding abortion.

I have friends who have done sidewalk counseling; one of them also has engaged in rescues.435 For various reasons—one of which admittedly is cowardice—up to now I have been unwilling to do either of those things. My friends think I am failing to do my duty. The one who has been involved in rescues argues that everyone has the same duty to try to stop abortions as to try to stop the killing of an already-born child, the only difference being that the Supreme Court’s ukase has made abortion legal.

While I see the force of his argument, it seems to me to prove too much. Specifically, it seems to point to a duty to gun down abortionists—something a few people have done, but hardly anyone approves of, much less regards as a duty. Let me explain. My work as a visiting nurse sometimes takes me into rough neighborhoods at all hours. After one bad experience that I will not go into, I learned to use a handgun, got a gun and a license, and now carry the gun at all times in my shoulder bag. Suppose I am walking down the street and see a man brutally beating a small child with a baseball bat; I take out my gun and order him to stop; he shouts a threat at me, turns, and hits the child again. Surely, it would be right for me to shoot him, and, as I was taught to do, I would aim at the middle of his back to give myself the best chance of stopping him. If I killed him without using more bullets than necessary to stop him, I am sure nobody would object. But if everyone has the same duty to try to stop abortions as to try to stop the killing of an already-born child, then I have a duty to gun down abortionists.

While I would like to know what you think of the argument between my friend and me, I am more interested in the broader question: Does everyone have a duty to try to stop abortions?

Analysis:

This question calls for applying norms regarding civic responsibility and the use of force to protect innocent people’s lives. Everyone who recognizes the evils of abortion and its legalization should do something to oppose them. But since each individual has his or her unique personal vocation, each must discern what he or she ought to do. Prima facie, the justification of force to defend the innocent seems to extend to gunning down abortionists. Although arguments against doing so drawn from prospective bad consequences are not decisive, the action is unjustifiable insofar as, rather than being an effective means of protecting the lives of unborn persons, it is a revolutionary act that surely will not succeed.

The reply could be along the following lines:

Abortion and its legalization are great evils.436 They differ in some ways from the mass murders carried out under Stalin, Hitler, and others, but also in some ways are comparable to those crimes and in other ways even worse: because of the greater numbers being killed, their total innocence and defenselessness, the essential role played by those primarily responsible for nurturing the victims, the widespread support of this slaughter by both rulers and people in so-called liberal democratic nations, and the complicity in the killings of so many religious leaders, educators, people trained in law, health care professionals, people in the mass media, and so on.

Everyone who recognizes the evils of abortion and its legalization should do something to oppose them. What that should be depends on an individual’s unique opportunities and capacities. Opportunities—what can be done—are limited to what is morally acceptable as well as to what is possible in other respects; one’s capacities are limited by one’s other responsibilities. All of us should do what we can, that is, some of the morally acceptable things that are in our power and that we can do without neglecting duties that flow from other elements of personal vocation to which we already have committed ourselves or which, being inescapable, we have accepted as God’s will. So, for instance, the contemplative nun and the bedridden man in a nursing home ought to work against abortion chiefly by praying for divine intervention or by writing letters of protest, not leaving the cloister or sickbed to participate in your friends’ work at clinics.

Your friends’ commitment to their effort is commendable, but they and others engaged in a particular sort of activity against abortion, its legalization, or any other injustice should not think or say that everyone should do the same. Whether or not you should take part in their efforts, they are wrong in pressuring you. Conscientiously examine your opportunities and capacities and discern what you should do about abortion. Though your appropriate contribution might partly coincide with theirs, it also might well be entirely different.

As for your friend’s argument that everyone has the same duty to try to stop abortions as to try to stop the killing of an already-born child, your counterargument—that this would imply a duty on your part to gun down abortionists—might not move him. He might accept that implication and urge you to put your gun and your skill in using it to good use. Of course, he might say it would be wrong to aim at the middle of the back of the brutal man in your example instead of aiming, say, at his shoulder, and, likewise, that it would be wrong for you to kill abortionists rather than choosing some less drastic way of stopping them—for example, cutting off their hands. However, that would not address the issue your argument raises, namely, whether you are soundly applying the principles that can justify using as much force as necessary to defend innocent life. Prima facie, it seems sound, for you could gun down an abortionist with precisely the same intention with which you would shoot the brutal man beating the child: not intending to kill or even injure him, but only to stop him and protect the victim.437 Moreover, since in both cases those being stopped are engaging in objective injustices that should be stopped, in neither case would you be acting unfairly toward those you stopped, provided you used the minimally destructive means adequate to protect the victim.

Your friend could reply that, despite their common features, the two cases differ in other morally relevant respects. He might offer four arguments. First, that gunning down abortionists is hard to reconcile with the Christian gospel, which emphasizes loving even enemies and seeking the conversion of evildoers. A dead abortionist cannot repent; women prevented from obtaining the abortion they wanted are unlikely to be moved to repent by the abortionist’s death; and many hearts, reacting self-righteously against the killing of an abortionist, are likely to be hardened with respect to the slaughter of the unborn. Second, he might say it clouds prolife witness by making it seem that even those who oppose abortion approve killing people when they think doing so would serve some good end. Third, he might say that the cases of shooting abortionists have proved it to be counterproductive. It provokes a strong, negative reaction from most people and countermeasures by public officials that impede every other form of prolife work, not least nonviolent direct action such as sidewalk counseling. Fourth, your friend could suggest with some plausibility that violence against abortionists serves as a bad example for many sorts of extremists, thus contributing to an increase in the lawlessness and unjustifiable violence already common in our society.

You can, of course, point out in reply that none of those considerations is decisive, since the gospel does not entirely forbid the use of force to defend the innocent (such as the child being beaten to death with the baseball bat), and, although gunning down abortionists has some bad consequences, it also has various good side effects. For example, it bears witness to the truth that unborn babies are no different in human worth and personal dignity from people already born; it keeps alive the awareness that legalized abortion is morally equivalent to murder and not similar to other morally questionable practices and institutions tolerable in a generally good and just society; and it serves as an example of unselfish courage in a society pervaded by self-indulgence and moral cowardice.

Your friend might reply in either of two ways. He could accept the conclusion and concede that under appropriate conditions, which probably seldom occur, it is morally right to use as much force as necessary to stop abortionists.

Or he could point out another difference between stopping the brutal man in your example and gunning down abortionists. The brutal man is an isolated wrongdoer whose violence is afforded no protection by society and its institutions. But abortionists are others’ agents—they serve women who have decided to get rid of their unborn children—and both doing and having abortions are socially accepted, protected by law, and even, in some respects, supported by public policy. The fellow beating the small child with a baseball bat almost certainly will not be replaced if you shoot him. Thus, your effort very likely will achieve your good end of protecting the child. But if you gun down one or even many abortionists, the women who meant to use their services, and others who will decide to obtain abortions, certainly can—and almost all probably will—find someone else to kill their unborn babies. And while killing or maiming large numbers of abortionists might have a temporary deterrent effect on actual and potential abortionists, it probably would quickly provoke a well-organized public response. New governmental programs almost certainly would make doing abortions more lucrative and provide abortionists with special protections and privileges. Abortion probably would be at least as widely available as it is now, so that no fewer, and perhaps even more, unborn babies would be killed. Since our society already is deeply committed to the evils of abortion and its legalization, gunning down abortionists therefore would be pointless unless one went on to gun down the public officials who support abortion. But that would be starting a revolution with no prospect of success; and, like war generally, a revolution without a prospect of success is unjust to the nation, whose common good it injures rather than promotes. Therefore, your friend could conclude, gunning down abortionists is unjust, while nonviolent direct action—rescues, sidewalk counseling, picketing abortionists’ homes—is just.

But should you participate? Perhaps. More likely, it seems to me, your unique capacities and opportunities call you to make your contribution in some other way—for example, working to persuade other nurses to resist pressures to participate in doing abortions and/or using your knowledge and professional contacts to help desperate women find a suitable alternative to abortion.