I really need to come up with catchy/significant titels for these posts. Anyway, here's my response.
SLE vs. QLE is good enough shorthand. You asked what criteria I would suggest we use to determine “personhood”. For purposes of this discussion and to avoid this blowing up into a debate that involves euthanasia (though that could certainly be grist for future mills here) I would say that at the point the fetus becomes viable outside the womb is the point at which it has the rights of a person. Before then, which as best I can tell given current levels of technology is twenty-two to twenty-three weeks, I still believe that it is a person, but it becomes more difficult for me to tell someone that they are committing an immoral act in having an abortion. When a mother loses her baby naturally at a very early stage I would perfectly understand them mourning the loss. So I do believe that conception is the point at which life begins, but while they are completely dependent on the womb environment the rights of the mother take precedent. During that time it is as much a part of her body as any other. Once it is capable of independence, it should be granted that possibility.
When I talk about us being created in the image and likeness of God, I don’t necessarily mean that the more like God one is the more of a person they are. Considering I believe that God is so much more, infinitely more than we are, we can’t approach what God is. As such I don’t think that an adult is more like God than a child or if they are then it’s a matter of an infinitesimal difference. It comes back to that matter of potential, I suppose. In regards to a brain-dead individual, I would say that they are not like God of course since they don’t even have the potential to reason, emote, etc. So for me at least, one is either a person or one is not, there are no degrees per se.
So speaking of that let’s talk a little about potential. You talk about the likelihood for that argument to grant us fewer rights. After all, you say, you have the potential to be a corpse. I’ve often heard this brought up and I’d say that’s not a potential, that’s a certainty. In our culture even corpses have rights, but no one argues that you should have the same rights as a corpse, because a corpse is not a person. No one argues that they are, so this strikes me as a bit of a red herring. Now if the corpse had potential to become a person I could see an argument for giving corpses the same rights as a person, but not the other way ‘round. In my mind a fetus is a person, so the potential is not the possibility that they will become a person. It’s not a serious state change (dead to alive), but the idea that given time they will come to be someone just like you or I. It’s a matter of degrees. Even if that baby will come out with Down’s Syndrome, that doesn’t mean that they lose the chance to experience existence as best they can. When you say a” blastocyst has much lower of a chance of realizing its potential personhood”, I assume that you’re talking about statistical chances. For me that doesn’t really enter into the equation. I always try to assume what the best case scenario would be when I make a moral decision. If there is any chance that the baby can come to full development, then it should be allowed to. Of course things are never that simple and if, as in your examples of woman A and woman B, there is near certainty that it would cause a great deal of harm for a woman to carry to term, I think it would be morally permissible for her to abort so long as she did it early on. Of course, in my opinion it would be better for her to take every possible precaution not to get pregnant including, but not limited to sterilization.
I’d be interested in hearing more from you concerning the idea of suffering. What does it mean to suffer? Is it strictly speaking mental? If I were to assault someone who was unable to feel the pain physically, but was still mentally acute or vice versa is this different morally from assaulting someone who had all of their faculties? And while the mother can certainly determine her level of suffering, how certain can she be of what level her child is capable of? Should she always assume that her level would outweigh that of her child’s? I can’t help but think that this sort of reasoning could extend beyond the point of a child being born. If a two year old is causing their mother to suffer, should the mother be allowed to take extreme action to end it? And then you need to examine the mother’s ability to ascertain their own level of suffering. A fourteen year old doesn’t usually possess the tools necessary to make that assessment. Given that, would it be moral for a teenage mother to abort? So this adds another question to our discussion. It’s not just, at what point is it no longer moral to abort given the baby’s level of development, but also at what point does a mother lose or gain the ability to make that decision?