I do not consider what a pre-implantation blastocyst *might* become at some point in the future—I only consider its present characteristics. A person really only exists within a functional brain; without a living brain, there simply is no person.
Science does not and cannot answer questions of the soul. I would say that the Bible does not truly answer that, either. There was a time when the soul was considered to appear at the time of quickening—about 3 to 5 months into pregnancy, when the mother feels movement for the first time. And we now know that the embryo moves long before the mother feels it. You could just as well deem birth the point at which the soul appears, and justify it biblically.
That’s not scientific either. That’s personal prejudice. All science can do is observe, not confirm biases whether personal or political. “I don’t know” are the three most honest words in science.
Like my mother who has Alzheimer's.
Whatsoever you do to the least of my brothers...