1. I don't understand where the bolded comes from
2. Should we accept it as true, this really doesn't invalidate the argument. Yes it means that the embryo would be in a different category, but this could still be a sub-category of "human life with a soul"
Absent a religious framework, arguments are only based on what moral constructs we should accept as a society and renders it so that no one can claim that any one stance is absolutely correct. Things are only a matter of opinion, and society should collectively decide on what stances are most productive for them, just as we do with everything else as a matter of law. Personally, I think that this is not something which society benefits from an absolute codified determination for all.