The viability line

John Hart Ely in Democracy and Distrust was wary about judges having the responsibility to determine substantive questions of fundamental rights. But, within the area they are appropriately deciding, Ely was supportive of clear lines that helped to avoid arbitrariness. One such example was the "one person, one vote" rule that held that different districts in a state should have basically the same number of people.  A few justices accepted some differential if the rules set were reasonable, but this raised questions of line drawing.  A clear rule seemed best.

This principle was held to be a core reason for the viability rule in Casey, even after the other two parts of the "trimester" test was removed as too restrictive. Undue burden was not exactly a clear line, but the plurality was still worried about setting some clarity here, especially for a line set forth by a court, not a legislature.  Thus, they followed precedent as to the line (other than when necessary for the health or life of the pregnant person) where abortions can be banned.  Viability was a sound line too:

the time at which there is a realistic possibility of maintaining and nourishing a life outside the womb, so that the independent existence of the second life can in reason and all fairness be the object of state protection that now overrides the rights of the woman. ... The viability line also has, as a practical matter, an element of fairness. In some broad sense it might be said that a woman who fails to act before viability has consented to the State's intervention on behalf of the developing child.

Roe was subject more opaque (note the hedge):

With respect to the State's important and legitimate interest in potential life, the "compelling" point is at viability. This is so because the fetus then presumably has the capability of meaningful life outside the mother's womb. State regulation protective of fetal life after viability thus has both logical and biological justifications.

In effect, it seems like the Court decided it was a medical question to be decided by the woman and her doctor, viability the line that was the norm in that area. Quickening was the traditional line, but that was largely practical -- it was when a life could be felt.  Roe discussed the point, including the positions of various religious sects, such as forty or eighty days being the moment when the soul enters, arguably a sign of "personhood."  A few years later, the Court reaffirmed that viability was a medical question, not a set legislatively set date.  Such flexibility troubles some, in part since it is in part a matter of local resources, and would change as medical science does.  But, it only changed a bit in over forty years.  When it drops to let's under twenty weeks, we might have to talk.

Blackmun also in time had a firmer grasp on things:

The viability line reflects the biological facts and truths of fetal development; it marks that threshold moment prior to which a fetus cannot survive separate from the woman and cannot reasonably and objectively be regarded as a subject of rights or interests distinct from, or paramount to, those of the pregnant woman. At the same time, the viability standard takes account of the undeniable fact that, as the fetus evolves into its postnatal form, and as it loses its dependence on the uterine environment, the State's interest in the fetus' potential human life, and in fostering a regard for human life in general, becomes compelling. As a practical matter, because viability follows "quickening" -- the point at which a woman feels movement in her womb -- and because viability occurs no earlier than 23 weeks gestational age, it establishes an easily applicable standard for regulating abortion while [p554] providing a pregnant woman ample time to exercise her fundamental right with her responsible physician to terminate her pregnancy.

See, both Webster and his separate opinion in Casey.  What other line should we use?  The issue here is fetal pain, but as noted by the article just cited, if anything, that happens in a true sense after viability.  And, if the embryo or fetus cannot survive, what, the woman has an obligation to serve as a holding device until survival is possible?  Some suggest sentience is proper line, but not only is it harder to tell when that occurs, that too very well might occur around this time or later.  To me, there is a practical value to draw the line where there is meaningful chance for survival, even if the fetus has to grow a bit more in an incubator to survive on its own.  As the article notes, there is going to be close cases where survival is very slim, and if at all, major abnormalities will occur.  The word "meaningful" is somewhat tricky. But, viability still works.

So, I'm not sure what other line is to be used here.  As Stevens noted:

I should think it obvious that the State's interest in the protection of an embryo -- even if that interest is defined as "protecting those who will be citizens," ibid. -- increases progressively and dramatically as the organism's capacity to feel pain, to experience pleasure, to survive, and to react to its surroundings increases day by day. The development of a fetus -- and pregnancy itself -- are not static conditions, and the assertion that the government's interest is static simply ignores this reality.

This also is partially a matter of social judgment: there is a reasonable debate among people over the proper lines here, a plurality at least supporting abortions for various reasons in the first trimester, and leaving open later ones for special occasions, "special" often likely to be "mine."  Doesn't mean they think embryos and fetuses aren't in some fashion "human" or even (though less so early on) "unborn children," but not in a full sense of human personhood.  If the embryos or fetuses in some fashion had brain activity, this wouldn't likely change -- it won't be enough.  Also, there is an understanding that there needs to be some time here to choose an abortion, including later on in cases of fetal abnormality or limited other reasons.  A line too early clashes with this.

Most abortions occur long before viability, but as noted, there is a small number that are close to or after the line (we are speaking something like 1% here over twenty weeks).  This is not a trivial number in a raw sense, given the millions of abortions over the years.  Just to keep that in mind. Still, some do arise and the viability line works.  If fetal pain is an issue, and it will not unduly interfere with legal abortions, it might be warranted to use anesthesia.  Twenty weeks, as the article cited above notes, is a dubious line even in that respect.  And, a ban even less so.  It isn't even necessary granting the premise. Amounts to be bad for various reasons.

Troublesome abortion regulations often are a question of special rules where neutral medical rules would work just as well, except as a bias against abortion choices.  The concern here for the fetus is clear, but even on that level, a ban is not necessary.  Depending on your goal.