As always, thank you TaxingMatters for the detailed response.
I had not considered whether the Constitution forbids murder, as it always seemed implied in numerous ways (even knowing that the gov't alone is responsible for upholding the tenets of due process, it makes me think that a citizen would need justification/a lawful intent in order to deprive someone of their life and thus their freedom and property). Also, murder is a crime at common law and our Constitution derives from many; add to this the 9th Am's unenumerated rights clause and it seems that murder is outlawed in various ways. I would disagree that a state could repeal its homicide laws.. unless you're also saying they'd immediately be replaced with something that still regulates and defines murder.
You mention the possibility of an equal-protection challenge with regard to a typical person-person murder versus an unborn person-person murder. A good point; the actors are very unique in a pregnancy. That's why I offered the "stranger falling off a cliff" scenario, because I couldn't think of anything else, even having been a pregnant woman myself. It reminds me of a case which I think comes the closest to showing how a defense-of-self justification to allow/necessitate the death of another has at least some precedent, see McFall v Shimp (1978) http://www.ucs.louisiana.edu/~ras277...ol/mcfall.html
"In preserving such a society as we have, it is bound to happen that great moral conflicts will arise and will appear harsh in a given instance. In this case, the chancellor is being asked to force one member of society to undergo a medical procedure which would provide that part of that individual's body would be removed from him and given to another so that the other could live. Morally, this decision rests with the Defendant, and, in the view of the Court, the refusal of the Defendant is morally indefensible. For our law to COMPEL the Defendant to submit to an intrusion of his body would change the very concept and principle upon which our society is founded. To do so would defeat the sanctity of the individual and would impose a rule which would know no limits, and one could not imagine where the line would be drawn.
"For a society which respects the rights of one individual, to sink its teeth into the jugular vein or neck of one of its members and suck from it sustenance for another member, is revolting to our hard-wrought concepts of jurisprudence. Forceible extraction of living body tissue causes revulsion to the judicial mind. Such would raise the spectre of the swastika and the Inquisition, reminiscent of the horrors this portends."
You say in a pregnancy, the woman has no reasonable grounds to believe she is in imminent danger, and I'd have to disagree. There are a multitude of categorical dangers that increase drastically during and after pregnancy, anything from preeclampsia to postpartum depression, or escalated domestic violence and barriers to medical care. And the fact that a woman who delivers a live child will be thereafter duty-bound to provide care for a minimum of eighteen years, with the exception of adoption, either of which are often traumatic and life-altering. Freedom-altering. "..researchers calculated that in 2014, nearly 24 mothers died per every 100,000 live births across 48 states and Washington D.C., excluding California and Texas. The figure represented a 26.6 percent increase from the rate seen in 2000, which was nearly 19 deaths per 100,000 live births."https://www.google.com/amp/www.medicaldaily.com/maternal-death-rate-us-2016-its-only-gotten-worse-2000-new-study-finds-394630%3Famp%3D1I believe that these threats are reason enough to refuse saving the life of another.
As to involuntary servitude, which “necessarily means a condition of servitude in which the victim is forced to work for the defendant by the use or threat of physical restraint or physical injury or by the use or threat of coercion through law or the legal process," I must ask:
If abortion were illegal, how would the laws work? In practice, a woman who sought to kill her unborn child would probably need to be forcibly restrained, to prevent harm. Maybe even to prevent her from fleeing to another state where abortion is legal? Would she need to be restrained/monitored during childbirth? Would she have any say in medical options during such? How is that not a type of involuntary servitude contemplated by the 13th Am? And why make a distinction: "Neither slavery NOR involuntary servitude"? (Maybe it's to distinguish between territories where slavery was yet legal and those where slavery was unlawful but still practiced?) Even then, there have been comparisons drawn between the oppressive measures taken against African slaves and women of all ethnicities, as historically both were underrepresented and denied rights.
The Constitution says nothing of Africans specifically, it can only be inferred that at the time, their aim was to free African slaves. The certainty of the Amendment rests in the prohibition against slavery and involuntary servitude of any person, not just Africans.
Please recall also that during a time when women were not allowed to vote, keep their own wages if married, have bank accounts or own real estate, it was often a woman's prerogative to survive by securing a husband. In many many jurisdictions, refusing one's marital duties, like having sex, was and grounds for divorce. Thus, a woman's greatest prospect was in granting a man unfettered access to her body, often resulting in perpetual child-rearing. Woe be to the religious household that typically condemned birth-control and abortion. A woman's rightful place in society was that of a silent servant until "radicals" demanded equality, most basically resulting in women having a CHOICE to pursue their own happiness, whether through a career or family.
But please tell me about the real mechanics of oppression and forced servitude, as I have no doubt that the men who wrote the Constitution failed to consider the plight of their own American wives as they left open to future interpretation the meaning of involuntary servitude.
It becomes involuntary when the woman changes her mind about carrying the pregnancy to term. Same way sex can become rape. The Constitution embraces individual freedom, and that must include an assurance that one's new legal decisions will be respected inasmuch as they should mitigate the final result. No one else endures such risk and finality as in this apparent contract between woman and child.

