This Reply doth most certainly warrant Further Reply. Quoth Greg:

Thanks for this! I will now shamelessly take the bait.

Although I share your appreciation for the improvement that the Middle Ages represented as compared to what came before, I cannot refrain from saying that the battle against bigotry does not seem to me to have reached its apex at that time. [Insert clichéd, oversimplified and historically half-literate references to medieval marginalization, abuse and torture of outsiders here]

It’s also worth noting that we owe our knowledge of the personhood of the embryo entirely to modern science. Thomas Aquinas condemned abortion on grounds that it was contraceptive, because he did not know it was homicide. If you’re glad that you know the embryo is an infant human, thank Francis Bacon.

(source: This Exam Only Needs One Question | Hang Together)

Hah!  Bait strictly accidental, sir.  I couldn’t consistently speak my mind on the subject without putting it that way, although I almost edited it out because I realized it might accidentally resonate with a remark you made in your post about “natural rights” at ETS.  (I’m sorry I didn’t try to attend, now that I know you did.  I may well try to put together a paper for next year–I’ve kept my membership, but haven’t had opportunity to make much use of it, lately.)

As I plan to make a post soon about the “downstream from culture” point and the controversial status of “natural rights” logic in religious discourse (and how “fundamental human rights” and “civil rights” may complicate that picture), I’ll disengage your riposte to my “Christendom” remark as follows:

First, I suspect that we, being both half-breed children of the Enlightenment and Christendom, would agree that the hegemony of post-Christian Western thought has produced evils that even the ancient empires could scarcely rival:  the rationalist regimes of the 20th Century, and their quasi-religious totalitarian counterparts, and even the wars of the supposedly englightened nations, more than keep up with the corvee labor of the Egyptians, the genocides of the Assyrians, or the wars of the Macedonians and Romans, Huns and Vandals.  If you prefer the 17th to the 13th Century, I still hardly think you’ll prefer Mao or Margaret Sanger (or Attila or Peter Singer or Alexander) to Aquinas or More (or Locke or Burke).  And if you prefer to see Aquinas as a swerve on a path that leads more truly through Locke, and I have come to see Locke as a swerve back toward a path more truly drawn forward through Aquinas, then we only prove that we are half-breeds, as our common cause in the post-Christian West is our repudiation of its most distinctive strains in favor of those elements most attributable to its Christian patrimony.

Further, I cannot imagine in what respect Aquinas, Bacon, Locke, or pretty much anyone even tangentially related to the tradition that ran through Aquinas could find themselves at odds on the point in question.  As you say, Aquinas and Christians generally got the moral question right (the moral difference between contraception and abortion is real, as is the moral difference between blasphemy and sacrilege, but less important than the truth that these are all acts that pit us against the gracious work of God, and cut us off from its merits and benefits), quite without benefit of more recent science.  It beggars belief to imagine that the protege of Albertus Magnus and great Dominican defender of Aristotelianism (against a settled Platonist reduction of Augustinian theology that had repeatedly proved vulnerable to dualist misinterpretation) would suddenly *reverse* the course he had charted in theses that were mistakenly (and briefly) condemned and in his controversy against the “double truth” theory of Siger of Brabant; he would hardly suddenly decide that honest understanding of nature was *not* coordinate with honest understanding of revelation!  You can’t have Francis Bacon without Aquinas, the better-formed product of the same 13th-Century University of Paris that produced the brilliant but troubled Franciscan Roger Bacon (and the route forward from Aquinas would have been better if Scotus, Ockham, and others of the Schoolmen hadn’t been so radically deficient in their understanding of his synthesis).

In sum, Aquinas believed, based on the best science available to him, that “quickening” was the point at which a truly human being–a living soul–was verifiably present in a woman’s womb.  In slightly different ways, so did Augustine and St. Jerome, if we are right to rely on popular snippets of their more obscure works.  All roundly condemned “abortion” thus [mis]understood as contraceptive rather than technically homicidal, and all considered abortion homicidal at least from the moment human life could be detected by ordinary means, so it’s really a question of using scientific data to help us decide *which* mortal sin to avoid and *how* to help heal the guilty soul).  I can conceive of no morally or scientifically significant difference between refusing to even vote on the Pain-Capable Unborn Child Protection Act and refusing to even vote on the Kicking Unborn Child Protection Act.

In any case, I know that you will unhesitatingly agree that none of this in any way exculpates the post-Christian West insofar as, with modern embryology to tell us better, we not only refuse to accept the data when it leads us more certainly to more correct conclusions about the humanity of infants, but also enshrine as a “human right” the willful and publicly-funded slaughter of these innocent, language-learning, pain-capable, helpless humans.

Whoever knows what is right to do and fails to do it….

(source: James 4:17 RSVCE – Whoever knows what is right to do and – Bible Gateway)