Why did Jesus suffer for sinners and not victims

[Belacqua]

placing of such significance upon a single event.

I think the desire here is to find an ontological point of change -- something which isn't subjective but scientific. Then, you're right, the significance we give that change may vary. If people want to acknowledge that the ontological change is at that point but it isn't significant for them, that would be a different argument. 

In fact I think that the pro-choice side would do better to acknowledge that scientific issues of ontological change aren't included in their argument, only utilitarian and practical concerns. But I don't think that denying fertilization as a biological change is the best way to justify legal abortion.

It's obviously true that every event, including making a baby, has multiple causes. The question to me is whether, due to all these causes, we can define a point at which an ontological change occurs. 

Sometimes we obviously can't -- as in a Sorites Paradox, some conditions just don't have dividing lines. 

A better example here might be the construction of an airplane. The causes for the plane are many, including the investors saying to go ahead, and the designs, and the construction of parts, and the transportation and then assembly of parts. I acknowledge that there is no single point in the process at which the thing goes from being a non-plane to a plane. 

We could make a checklist of factors which make the plane flyable -- viable as a plane. The wings are necessary, but the seats and toilets aren't. So we could identify a day on which the plane went from flyable to non-flyable. And I think that some people want to apply this type of thinking to humans. They have a checklist of factors (self-consciousness, or the ability to survive outside the womb) which they take to be the difference between non-viability and viability. 

That doesn't, though, mean that the case of the plane and that of people are the same. It doesn't mean that viability and being a human are the same. 

Also, we could say that, for example, the causes of my death are already in place. Telomere shortening due to my age, my extreme espresso addiction, etc. But that doesn't mean that I'm dead already. Or that the moment of my death won't be a single, ontological change. Fertilization is this way, I think. The causes may be many, but there is still a single event of change.

I think personhood is the issue here. When can we say that what exists (whether it be a collection of cells or a zygote) is a person and has what moral rights may be granted by personhood? That's the ultimate question.

And a person isn't defined as "that which follows naturally from one discrete object." Of what does "personhood" consist? My example with totipotent cells showed that instead of one, two or more people may come to exist from the state of those cells existing, and that potential individuals will either come to exist or NOT come to exist based on what happens to those cells in that state. Nothing before or after that process can create THOSE specific persons.

I don't think I said "that which follows naturally from one discrete object." I think I said that a human being is a single discrete object with the necessary genetic material. A person isn't the act of meeting or the act of sex. A person is a thing which is discrete and has the required genetic material. That's what's new at fertilization.

But I agree, the debate over legal abortion is about personhood as a legal definition. Which may be different from biology.

If the discrete existence of an individual object with the required genetic material isn't the definition, then by what standards do we judge? I can see that for practical or even moral reasons we might prefer different boundaries. But there we get into milestones that are every bit as arbitrary as (you claim) fertilization is. Does personhood begin with consciousness? Is an unconscious person not a person? etc. etc. Is a slave a person? Could the government revoke personhood for some reason? 

I stick with my view that biologically, ontologically, the change comes at fertilization, and the rest is development of that thing. The argument that the thing is ontologically different before it's born (a fetus) than it is after it's born (a baby) is nonsense. It doesn't change its state due to location. While it's coming out of the mom it isn't half baby and half fetus. 

Whether people want to grant legal personhood, with rights, to the thing immediately after its ontological existence has begun, or later, is what the debate is really about.