In Vocab's final part, he talks a bit about the work that he and his wife do in caring for foster children. I commend him for that work, which is all-too-rare among opponents of abortion.
Thanks, Vocab, for the debate--and I still would like to hear a response from you in the comments on some of the issues that have been left hanging (e.g., in the comments on part 3).
UPDATE: It would probably be better to end this discussion with a summary that I already made in the comments on part 3:
We don't disagree that there is continuity of organism (just as there is continuity of a population of organisms over time)--all life on this planet is connected in that way. But just as we don't count every species as human, even in our own genetic lineage, we don't count every life stage of individual human organisms as persons. There's a sense in which "I" was once a zygote that had my same DNA, but at that stage there was no "me" there yet--there was nothing that it was like to be a zygote, to use Thomas Nagel's expression. In that same sense that "I" was a zygote, "I" will be a dead body in the future, even though there will at that point be nothing that it is like to be me, and the person that I am will be gone from the world though my body will briefly remain.
I think we understand each other's positions. You think that being a human organism is the same thing as to be a person, while I think personhood is a feature that comes into existence and persists for a subset of the life of an organism, that requires capacities of sentience or self-awareness.
But I think I can give reasons to support why my view makes moral, legal, and practical sense, and why human cultures and practices are more consistent with my view than yours. I don't think you can give such reasons, other than the brute assertion that human organisms are persons from start to finish. Your view has no need of the notion of person, yet it seems to me that there are all sorts of practical, moral, and legal reasons why we do need and use such a notion.