If I understand you correctly, you are claiming that personhood, in practice, is a binary variable; either one is a person or one is not. You deny meaningful degrees of personhood because your basis of comparison, God, is infinite. Since God has so much more personhood than anyone else, the minor difference in personhood between two humans is negligible.
But if we follow this reasoning a little further, I think we will reach a conclusion unacceptable to both of us. We would be forced to equate our personhood to that of a dog, for instance. After all, when we consider the difference between our personhood and a dog’s, it is nothing in comparison with God’s infinite personhood. Denying degrees of personhood between humans based on comparison with infinite personhood also denies degrees of personhood between species. A proponent of SLE would be forced to conclude that humans are not deserving of any special moral consideration based on our likeness to God. I assume that you do not agree with this conclusion thus you must accept that the premise is faulty. Therefore meaningful degrees of personhood (or God-likeness, for the religiously inclined) exist between some humans.
You do have a valid point in your rebuttal to my ‘potential corpse’ reasoning. The state-change from living to dead is (often) such a drastic difference that moral comparisons may not be applicable. Still, the argument for potential can be used to justify the restriction of rights. All of us have the potential to become senile, yet no one claims that we should have the same rights of the mentally incompetent. Again, I can see potential playing some role in moral considerations, I just don’t know exactly what it is and am hoping you can shed some light on this.
This leads me to another train of thought. I’m confident that you would agree that one who is senile is still created in the image and likeness of God (a person), yet we don’t grant them the rights of a mentally capable adult; the power of attorney, for instance. Nor do we grant equal rights to children based on their potential to become adults. If not degrees of personhood, what criteria are you using to justify the differing moral rights?
You legitimately ask me to define my use of the term ‘suffering’. Since my QLE is rooted on this concept, I should have carefully defined it at the outset. Suffering occurs when any entity cannot fulfill any of its interests. Anything that lives has an interest in not dying, anything that can feel pain has an interest in not being in pain, anything that is hungry has an interest in feeding, etc. An otherwise normal person who cannot feel pain has only one less interest than the rest of us, that individual doesn’t have an interest in avoiding pain. He/She will still have an interest in avoiding injury, scars, bruises, wasted time, the emotional impacts of being a victim, and so forth. Thus assaulting this individual would only be marginally less immoral than anyone else.
Another question you asked is how a woman can determine the level of suffering her fetus is capable of. Well, we need to take into account the varying interests at play here. As a living thing, a fetus has an interest in living and, after a certain amount of development, a fetus has a central nervous system and has an interest not experiencing pain, but that seems to be the extent of it. I know of no evidence of any other interests of a human fetus. An adult woman, by way of contrast, has both of these interest plus many more, such as an interest in avoiding the pain, expense, inconvenience, emotional hardships, and health risks of childbirth. Her multitude of interests trumps those of the fetus.
Using this version of the QLE, it is easy to see why a woman’s prerogative does not extend to after the birth of the child, at least not in our modern society. The main suffering a postpartum mother would experience result from the on-going care of the infant. Infanticide is not justifiable because our society provides an alternative that does not infringe upon the infant’s interest in survival and does not require the mother to assume additional suffering; adoption or foster care. There is no question that these options are morally superior to infanticide since they reduce the suffering experienced by the infant without significantly increasing suffering for any other person. For this reason, post-birth is the rational point to grant a human a moral right to life.