The idea of life at conception

[True Federalist (진정한 연방 주의자)]

The real question is personhood (for law), and presumably for religion it would mean have a soul breathed into it by God in the image of God?

Personhood is the real question. The pro-life/pro-choice debate (mostly) comes down to the philosophical/religious question of what a person is.

And it's one that can't be answered objectively, which is why altho I favor legal first-trimester abortions, I think Roe was a bad decision. The subjective question of personhood needs to be left to the legislative branch, not the judicial branch to decide because under our system of separation of powers, the job of deciding what is the answer to subjective questions belongs to the legislative branch(es).

[True Federalist (진정한 연방 주의자)]

The real question is personhood (for law), and presumably for religion it would mean have a soul breathed into it by God in the image of God?

Personhood is the real question. The pro-life/pro-choice debate (mostly) comes down to the philosophical/religious question of what a person is.

And it's one that can't be answered objectively, which is why altho I favor legal first-trimester abortions, I think Roe was a bad decision. The subjective question of personhood needs to be left to the legislative branch, not the judicial branch to decide because under our system of separation of powers, the job of deciding what is the answer to subjective questions belongs to the legislative branch(es).

The question, whether answerable or not, if personhood exists as an entity at all, cannot be subjective. That's sort of the point. If a person has a certain objective value to it, then regardless of whether we call it a person or not, if it has that objective value (substantial form) then it is a person and if not, then it isn't.

The US system isn't really setup to deal with such questions at all but rather is based on consensus, but I do agree the legislature is better suited to answering it than a Court, especially given the Court has no specific authority to address the question given to it by the Constitution and will thus simply rig the arguments to come up with the conclusion it would like.

The question of what constitutes a person is subjective. Once that subjective question is answered then whether something meets that answer is for the most part objective.  Even once we had a subjective answer, there's still the question of whether the grant of personhood only extends to those that definitely meet the criteria chosen, or to all who it cannot be shown do not. (The latter is tricky as it could end up granting personhood to some non-human species such as cetaceans, octopi, and the great apes if the definition does not include a requirement to be of the genus Homo.

[True Federalist (진정한 연방 주의자)]

I think ontology is important here.

First of all I've always found an irony in say, bodies like the Catholic Church making appeals to embryology as a scientific support for its position given what the study of embryology actually entails. Fetal personhood as a modern day ontological concept is only possible because people can actually see whats happening in the womb in it's earliest stages. Which as a pursuit of scientific understanding, involves the destruction of embryonic 'life'. Likewise with the backwards march of viability (which no one who is pro-choice has much issue with) due to advances in neonatology.

But that's not really what I take issue with. Ultimately what concerns me, is the pursuit of defining 'life' by some medical or scientific definitive point by which one can then martial morality around. This turns pregnancy and it's impact on a mother from what is a human experience, a female experience to something outside of that. I think many pro-life advocates are terrifyingly bleak on that proposition.

If you define 'life' at conception, then armed with the fact that 50 to 80 percent of even implanted embryos spontaneously abort, then those spontaneous abortions are the ending of a 'life', without anyone's knowledge. Something that happens as a natural cycle. This is before we even get to known miscarriages later in a woman's pregnancy. These are now 'deaths', even if you want to treat them or categorise them differently. You are then saying that the womb, that a woman's reproductive system effectively is a place where death occurs far more often than life. That's a dangerous psychological route to go down and a worrying subversion of womenhood and pregnancy.

Even from a scientific perspective there isn't a neat consensus. Gastrulation for example is the point at which an embryo can no longer divide to become identical twins. It can no longer become more than one thing. Surely before that point, then all that embryo is, is a 'potential'; potentially one thing, or two things or three things or nothing. I think Anthony's point on life v existence above is quite an important one.
 
I've always felt that the person who is pregnant should get to decide when it's a person and everyone can have different understandings of that and not be morally or legally judged. Which seems to be a strangely radical proposal these days.

A person's psychological health is vitally important to them. Pregnancy can be hell for women. For many women who fall pregnant, psychologically there is 'no child'. It's just a state of being. If a woman is pregnant and does not see it as a person, and does not wish to be in 'the state of pregnancy' and that is causing her psychological distress, then she has a right and her doctor has a right to respond to that harm.

Waving development charts about and talking about 'life' and being so clinical or scientific about what is happening inside 'women like her' without actually caring about whats happening inside her (and how she is responding to this) is of absolutely no relevance and no help to her. At worst, dismissing her psychological concerns in some weird utilitarian fashion, demanding the child be carried to term, then taken away from her if she doesn't want it, simply adds what could be a life long psychological response to pregnancy, delivery, post natal responses and removal of the child, onto what was already pre-existing.

To a large extent I agree with you here. Where I differ with you is, as usual, over the absolute priority you seem to give the individual, without any concern of the effects of actions on society. Or rather, on your apparent assumption that one can maximize social good by having a society where each individual is free to act to maximize their personal good. It's a good starting position, except for your point of view that if a woman doesn't think that if what is inside her is not a child, then it isn't one, regardless of the views of others. That sort of logic can easily lead to the justification of dehumanizing various groups of humans. It's why the individual perspective should be the starting point, not the finishing point for determining social positions.

My own viewpoint is that personhood begins at some point between when the embryo becomes a fetus and viability. I don't have any strong views on where therein to define the point where under the law a life becomes a human life. Biblically, quickening might seem like a good point except we now know that the perception of quickening does not happen in every pregnancy at the same point of fetal development. Still, the fact that point rather than once a pregnancy was known to be was used seems a strong argument to me against claiming conception as the point for those arguing from religion.

[True Federalist (진정한 연방 주의자)]

I believe neither that society is inherently good or evil nor that individuals are inherently good or evil. Relative benevolence is not a factor here. Rather it is that individuals don't function in isolation. They are part of a society, and thus restrictions on individuals that benefit society as a whole are generally a good thing. (I'm aware that not every such restriction put forth with that claimed goal actually is beneficial to society as a whole.)

Not only that, but I doubt that even you would argue in favor of allowing infanticide if a woman gave birth yet felt no connection to the infant. So clearly there's something beyond the woman's point of view to be considered in deciding when a life becomes a human life. Something determined by society.

[True Federalist (진정한 연방 주의자)]

I believe neither that society is inherently good or evil nor that individuals are inherently good or evil. Relative benevolence is not a factor here. Rather it is that individuals don't function in isolation. They are part of a society, and thus restrictions on individuals that benefit society as a whole are generally a good thing. (I'm aware that not every such restriction put forth with that claimed goal actually is beneficial to society as a whole.)

Not only that, but I doubt that even you would argue in favor of allowing infanticide if a woman gave birth yet felt no connection to the infant. So clearly there's something beyond the woman's point of view to be considered in deciding when a life becomes a human life. Something determined by society.

When a woman gives birth the baby is clearly a human with associated rights. I'm talking about defining personhood before the point of viability which I think rests with the mother. I have no idea what you are trying to argue about.

While there's no place today that I'm aware of that condones infanticide, historically that hasn't always been the case. To argue that birth makes someone clearly human is not self-evident, but a societal norm. A norm I'm glad is a norm, but to pretend it's not a norm is to pretend that your subjective viewpoint is objective. Unfortunately, abortion is one of those issues where a lot of people on all sides make the mistake of presuming their subjective position is an objective one.

I'm not Ernest, but I think he is saying that "mother's connection" is a too arbitrary standard. It would lead to the absurdity of Baby A and Baby B having more or less identical characteristics (heartbeat, feel pain, whatever), yet only one would be a person.

Pretty much any definition of when a human life begins is going to be arbitrary, be it the physiological definitions that generally are the subject of the abortion debate or the physiological definition Andrew is giving. My objection is not over it being arbitrary but his position giving absolute preference to individual concerns regardless of societal concerns.

[True Federalist (진정한 연방 주의자)]

"A foolish consistency is the hobgoblin of little minds, adored by little statesmen and philosophers and divines." — Ralph Waldo Emerson

Devising an identical measure for both the beginning and end of life is no less arbitrary than any other.  In part that's because I can't think of one that would not ignore the difference in future potential that exists at the beginning and end of a human life. Or ignore the importance of existing attachments with others that that life be it human or not, has.