Sigh.. I don’t think you’ve said anything I disagree with. Of course a human being is human being from the point of conception.
The question was: is there a stage at which a human being is not yet a person, and thus not yet entitled to the full rights of personhood?
The answer to that question is not obvious to me. Fetal development timelines do not answer it. Fetuses may dream and cry, but that doesn’t answer it either. (Puppies dream and cry). I don’t really have the patience to debate this point, as I think it ultimately boils down to belief or disbelief in the soul, which is the domain of religion.
I support the pro-life position because I’d rather live in a society that views all human life as sacred, even if i find that view irrational.
P.S.: Okay, I was wrong to call embryos unicellular. I should have said “zygote at the moment of becoming diploid” i.e. conception.
From a legal standpoint, none of that matters, because we should err on the side of caution where we don’t know.