Just because something is not logical does not mean it is not rational. For example, my argument from state duties is from ethos and is rational. That is not to say that end results are not important. An argument from end results does not mandate a certain form of persuasion.
You need to grasp what the end results are first to know what you're choosing in the first place, regardless of ethos. It's not the kind of thing one would want to enforce in ignorance of the consequences.
Rather than mandating form of persuasion, it's a necessary step to have a viable basis for making a conclusion in either direction, or a different one entirely.
Is the fact of the matter that you're placing a burden on a living person (or large numbers depending) to keep something alive that, as of yet, doesn't have the ability to perceive pain or loss? Or is the fact of the matter something else? Even an argument from ethos isn't going to fly if you can't pin down facts.
Being forced to carry a pregnancy to term is a far greater violation of bodily autonomy than any organ donation.
No doubt, given the physical implications. But it doesn't stop there either, and ultimately the autonomy violated could extend past the mother as well depending on the circumstance.
Once you give yourself the 'right' to define the 'role' of things, then you can just win all the arguments by assuming the conclusion.
No joke. "Nature" doesn't care, either. There are no "roles", that's a contrived human conception of reality. Reality is still what actually happens, and there is nobody who "designed" nature to the best of our evidence-based knowledge. As such, arguments that hold for early-term fetuses should also hold for skin cells, cloning, and sperm/eggs...all examples of "potential sapience" that are missed, and in inconceivable quantities too!
But none of that inconvenience matters if one simply assumes the conclusion.
