In their attempts to justify abortion, and more recently, infanticide (re-branded as post-birth abortion - you really can’t do satire any more...) ethicists and others rely a lot on notions of personhood.
The idea being if someone isn’t a person, you don’t need to accord them the rights of personhood.
I think this is a problematic approach for many reasons. One is that the whole notion of personhood is contested, and is necessarily subjective - a matter of opinion. But on the basis of it, they are prepared to kill.
A second is that I dispute that it is a relevant discussion. The minute one person (or group of professionals, or even society) starts to decide who else is or is not ‘a person’ we open the doors to all sorts of inhumanity. Indeed, it is only done for that reason: we know well enough what a human being is.
Notice the shift in language: from person to human. Because actually, what we believe in is human rights, not personhood rights. These are rights attributed to human beings. A human being is a category that can be empirically proven: whether by its provenance (the fruit of human sperm and human ovum) or its DNA, or a number of other objective processes.
The only purpose of the personhood debate is to muddy the water, and justify the unjustifiable. Even then it fails. Let us say, just for the sake of argument, that I am unsure whether an embryo is a person at 18 weeks; or that I am unsure if the brain-damaged child is a person; or that I am unsure whether the lad in a coma after a terrible accident is still a person. If unsure, then my moral duty must be to err on the side of prudence. To take an analogy, imagine that I am a scrap-metal dealer, about to crush a car. Someone says he thinks he saw an arm waving from the car window. I don't think there's a person in there - but surely I have the moral duty to err on the side of prudence and check. To proceed and crush the vehicle without checking would surely be wrong. So if there is a human body in front of me (whether in utero or not) and I am unsure whether it has person status, I should err on the side of doubt: the fear of the catastrophic injustice if I am wrong should stay my hand...
But all that is by way of digression. In fact, the fundamental principle applies: all human beings have human rights, and once we start to decide arbitrarily that some are non-humans, it is our own humanity we damage: and the results will be catastrophic, for us, for them, and for human society as a whole.