As a legal matter, murder is inter alia specifically killing that is illegal. Thus, simply by definition, abortion cannot be murder under a regime that considers abortion lawful.
As a further legal matter, there are myriad categories of homicide. We begin with the old Common Law distinctions between murder, manslaughter, and justifiable homicides like self-defense or those otherwise legitimately incident to say, police work or military service. Then, of course, the old Common Law terms are supplemented by the vaguely Continental criminal codes that have replaced (or more often, honestly, just rephrased) the old Anglo-American Common Law notions in federal and almost all state law. So we then get all sorts of codified gradations of “homicide” of various kinds, degrees, etc.
Now, in both the old Common Law and the present penal codes, it certainly does make sense to distinguish the illegal homicide that occurred due to unforeseeable accident, negligence, or duress (e.g., the killing of a wife-beater by his wife) from the “premeditated first degree murder” sort of homicide.
And I think that it’s this set of intuitions and discursive habits that pro-choicers are understandably bringing to discussions both here and in the wider public square.
Pro-lifers are usually no less conversant with the legal norms I’ve just discussed. But many of us also spend a great deal of time on the Talmudic parsing of Scriptural legal codes and on philosophical argumentation in the Greco-Roman natural law tradition.
In both of these contexts, one very prominent distinction that one encounters ubiquitously is that between “killing” and “murder.” It is a commonplace of discussions of the Decalogue or the Dominical sayings that one ought not interpret this or that Hebrew or Greek word for “murder” as though it meant “kill.” For instance, if you google “murder vs. killing” you’ll find that most of the first-page results will be about the commandment that “thou shalt not kill”—either the Fifth or the Fourth, depending upon one’s denomination.
In particular, just about everyone who has spent any nontrivial time at all reading debates between pacifists and just war theorists and other advocates for a (limited!) place for violence within Christian life in this fallen world will carry around in his or her head as a stock bit of mental furniture a basic familiarity with arguments about how “Thou shalt not kill” forbids murder in particular, and not all killing.
Thus, for the Biblically focused mind, it is both natural and contextually entirely legitimate to think of “murder” as being a broad term for all the various sorts of unjustified, wrongful killing (whether legal under man’s law in a given jurisdiction or not).
So while in the positivistic sense, it was not murder—because not illegal—under Third Reich law* to gas Jews, in the Biblical exegete’s sense, it was murder.
*(Nuremberg, of course, later decreed by an admittedly incomparably noble lie [but still a lie] that it had already been illegal under international law. That is beside the present paragraph’s point, which is merely to elucidate the illegal/wrongful distinction.)
Not only does this murder / killing dichotomy fulfill a real need in theological discourse, but it also reflects the spirit of traditional English speech and writing. It is certainly true that “murder” quite early in its development took on all sorts of specifically juridical associations. But the term itself is as solidly Anglo-Saxon as “killing,” and isn’t one of the always already merely legal terms that came into Middle English with the Law French of the Anglo-Normans.
To be sure, long before William conquered, the Saxon kings had law courts that distinguished murder from killing. Nevertheless, this ancient Saxon doublet fossilizes for us not merely the Thrasymachan conventionalist’s distinction between legal / illegal, but the pre-legal, logically and culturally prior moralist’s distinction between manslaying that is rightful and manslaying that is wrong.
In short, while the pro-choicer’s murder/homicide/killing gradations belong to Creon (and are appropriate enough in his sphere of positive manmade law), the Biblical exegete’s distinction belongs to Antigone (and to her wider sphere of the claims of natural and Divine law upon man’s laws.)
Thus, as is so often the case, the progressive is speaking for and from the assumptions of the City of Man, while the trad is critiquing them from a stance within and on prophetic behalf of the City of God.
When we say that abortion is murder, you hear us saying that it is first-degree intentional homicide and should be punished to the full extent of positive law. What we are actually saying is that, in contrast to self-defense, killing by abortion is morally wrong.
To ask us to abandon our millennia of tradition of discussing killing vs. murder in the way we do in order to conform to some Rawlsian canon of secular public reason in the naked public square is ultimately to insist upon making elite progressive discourse hegemonic over against subaltern voices like those of the Appalachian welfare recipient striving to read his Bible aright, or the blue collar retiree praying her rosary outside an abortion clinic. It is to say that the bureaucratic discourse of the Anglo-Norman attorney or the Vox infographic-composing glib Harvard grad must always condition and stand in judgment over the Saxon peasants jawboning by the town well or the black Pentecostals chatting in the barbershop, who know in their bones that some things are just wrong.
If you want to discuss whether the murder that is abortion is of the duressed sort that, like the murder of a wife-beater in his sleep, ought to carry a very light sentence indeed, then fine. That’s an important discussion to have, with nuances that are admittedly of grave import and need to be teased out.
But we pro-lifers are going to insist upon having that discussion in terms of kinds of murder, not in terms of “degrees of homicide.” That’s not incitement. It’s a subaltern dialect of English that contains all sorts of moral wisdom from regular folks that progressive elites ought to dignify as discursive peers, instead of dismissing them as hate-spewing trailer trash.