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?
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.
