You fall into tricky water when you start habituating your mind to arbitrarily determining something so abstract as personhood and when it begins or ends. Personhood is an entirely legal recognition of something. I believe you realize it is a recognition ; that is, it is the Law recognizing some reality outside and independent of itself, and affirming its existence.
You enter this problem : if personhood does not begin at the moment life begins, and demonstrably so (let's not kid, at conception there's an explosion of life and it's happening, and happening fast), when does personhood "happen" ? Is there some legal Incarnation happening ? Does personhood fall from heaven on a human being at some arbitrary point in time ? If so, pray tell what is the cause of this marvelous event, and when does it occur ? You touched on the danger and ambiguity of arbitrarily off-shoring this responsibility to a panel of experts or bureaucrats, for example, and the precedent of doing that is alarming. It puts terrifying powers in the hands of select individuals, powers of life and death, the rights of men or the abrogation thereof.
But let's hold to human custom and convention : a lot of couples, upon discovering they are pregnant (as it were), are over-joyed, and at once begin to grant the child a name or names. They draw up names for a male or a female, for example. Already, for these parents, personhood is established, and the humanity of the nascent life is unquestioned. Age is not even a factor of consideration. What's material is that life is there. We know, for example, that at the moment of conception a child is always either male or female, so trying to reduce the child to some "it," for the purpose of justifying abortion, is a serious factual error not a little expedient to the ends of the argument. The child, the fetus, is always either a male child or a female child, and never properly an "it."
Now Christians cannot, and will not, ever care for any of this brutish sophistry, for we have known the Truth far before scientists confirmed it. We know, according to our Scriptures and the Creed, that God "became incarnate of the Virgin Mary by the Holy Spirit, and was made man." That is, identity, gender, personhood - all of these questions were mute at the moment of the incarnation, which corresponds (biologically) to conception. That will not change for us.
The teachings of our religion is that when man divorces himself from God he falls into errors such as rationalism, and the consequence of these errors are the battles we now face, where we feel compelled to demonstrate every moral truth and argument by the arbitrary and capricious determinations of any given set of men. It is this fallacy that undermines the moral order and lends itself to such evil regimes as the Soviets and Nazis, who were not a little opportunistic of the aggrandizement of the state's powers and jurisdictions afforded by the widespread loss of belief in objective truths and the moral dogmas of the Church. These being evaporated, they left a huge vacuum that philosophy and intellectualism are constantly trying, in vain, to fill. Now Liberalism then as now dogmatically dictates that we Christians need to conform to its own fallacious presumptions and appease its own altar of rationalism before being permitted into its holy of holies and receive the blessing of its recognition of our moral precepts. So far our appeasement of this process has already cost hundreds of millions of lives in labs and abortion clinics throughout the world.
Let's be frank. Canadian law made a disastrous and dangerous swing by subjecting humanity to its fanciful curiosity - who or what is a human or who or what is a person ? My question is who or what is a Canadian court to determine who or what I so intimately am ? Needless to say, I reserve my right to rebellion against any government that presumes it will decide for itself whether or not I am a person or a human or whether or not my children may or may not be worthy of that right gone Animal Farm to a privilege. We are talking about legal errors and contradictions not a little reminiscent of those in the United States before the civil war. Apathy, at present, appears to me the only real difference, and for democracy that is a dangerous difference.
Now in your final argumentation you compare the loss of innocent human life as being comparable to the loss of a certain amount of blood or the loss of organs following death. Seeing as how the loss of a little blood is not liable to kill me nor will my organs being taken from my body following death change the fact of my beind dead, I am not a little inclined to find such concerns spurious in contrast to rather more important considerations as the saving of innocent life from the death penalty.
Pax,
Tim