Hi there.
it comes to viability, I would say that personhood is a misnomer. Personhood is generally associated with mental faculties. Furthermore, viability would then make personhood arbitrary and contingent upon medical technology of the time, which is continually advancing.
You’re right; I think the courts (in the Roe v. Wade decision) were making a compromise between the pro-life and the pro-choice argument, in privileging viability over questions of personhood (pro-life proponents would place personhood much earlier, pro-choice proponents conceivably later). I understand that a pro-life proponent believes it was a lousy compromise.
of the main arguments for personhood (and one which I mentioned in the thought experiment) would be desires. If one has no desires, then it seems the thought of being killed wouldn’t be all that psychologically detrimental to that being. They cannot desire to live, after all. They also cannot desire not to feel pain. However, it seems that laws against cruel and unusual punishment only apply to people who are already considered persons (correct me if I am wrong on this). If that is the case, then it seems one is already assuming that those in my thought experiment are persons, which is fine, but then, it invalidates the characteristics listed as viable reasons to believe a fetus is not a person.
It gets thorny. A zygote or an embryo has no desire to live, yet reasonably
would have a desire to live if it had the wherewithal to be conscious of its fate. You’re right; I think I am assuming, in my response, that the law indeed does “err on the side of caution” as regards the personhood of late-term fetuses, let alone newborns, and that this would carry over to your thought experiment. Questions of personhood are off limits there, or are irrelevant.
In a comparatively more innocuous way, I’m also thinking of the way that our laws “draw the line” in terms of who gets the right to vote; who gets to drive; who gets to drink. It would be ludicrous to give a two-year-old the right to vote (though I can’t say they wouldn’t make any less informed decision, than a lot of other vote-wielding citizens

).
So there’s the sense of, “a two-year-old is
obviously not a candidate to have the right to vote” (in the same way that, for some pro-choicers, a 10-day old embryo is “obviously” not yet a person). Then you start sliding the scale further and further over, until you get into a rather large “gray zone.” For example, are there not mature and intelligent 16-year-olds who probably
deserve the right to vote? Are there not 18-year-olds who probably are not yet ready, and should wait until at least age 21? Are there not 30-somethings and 40-somethings that probably shouldn’t have the right to vote at all? Should there be a particular IQ threshold for exercising the right to vote; for example, if someone is mentally disabled, should that right be revoked?
It’s irreducibly arbitrary, isn’t it? Someone who is 17 and 364 days is not legally authorized to vote, whereas someone who is 18 and 0 days
is. Did he magically become a “mature adult”, overnight? Can one p(name removed by moderator)oint the exact moment at which he merits being called an adult?
I think the courts realized that it is impossible to identify the moment that personhood begins, even though science can tell us the moment that
life begins. Their fatal mistake, I suppose a pro-lifer would say, is that they made an arbitrary distinction between a living organism that is genetically human, a living human organism, proper, and a living human person. The viability argument was a way to evade deciding on this question of the moment at which one becomes “a human person” even though viability itself is a gray area (sure, a 2-day old embryo is not viable outside the mother’s body, but a 7 month old fetus
may be).
then it doesn’t seem to make much sense to use any standard of personhood other than viability (disregarding my issues with it). Things like desires, emotions, etc would then be made irrelevant in being replaced solely by the viability argument.
It’s also true that viability is something which, strategically speaking, pro-life advocates are willing to run with. In a way, it is a boon to the movement that the moment of viability can be increased with further advances in medicine. It may be a technicality, but it could prove useful as medical technology continues to improve.
The issue of pain is also used strategically; if pain can be demonstrated, then one has a comparatively stronger case, against the skeptics, that a fetus is already “sufficiently” a human person. Of course, it’s no guarantee; I’ve heard arguments that, if fetuses are demonstrated to be capable of feeling pain during the first trimester, then fetal anesthetic will be mandated before an abortion is performed!
But if were demonstrably shown that even a first trimester fetus can experience fear, anxiety, terror, or agony, all but the hard-core pro-choicers would probably swing over to the other side.
It’s also fair to point out that governments, frankly, are not shining bastions of respect for life! Surely, innocent people have been unjustly imprisoned, and executed. The government errs on the side of caution in terms of someone needing to be proven guilty beyond a
reasonable doubt (which falls short of a standard of 100% certainty) ; then, there is a potentially lengthy appeals process, to which the condemned person is entitled. But governments are not as conscientious guardians of life as any deeply religious individual would be; during military operations, “erring on the side of caution” is also pretty loosely applied, in the sense that collateral damage is considered a legitimate casualty of war.