Geez, man! It's been damned near forty years since I took ethics and I find that my old book has hit that black hole where books are lost -- the bibliographical Saragasso, so to speak. While I have some Kant, it's not in his Introduction to a Metaphysics of Ethics, 'cause I looked. Might be a summarization of Berkeley's utilitarianism, though; I'll try to plow through it again. I'd email my old ethics teacher, but I think he died some years back. Too bad; he was one of the good ones.

You have heard that old saying, "If Kant can't, nobody can" haven't you?
Or what Descartes really said: "Cogito cogito cogito, ergo cogito cogito sum, cogito"?? (Ol' Rene wasn't always certain about things.)

Seems to me that the very best stem cells for use would be those derived from the person for whom they'd be used. Not because of rejection issues, but it just seems to me that this would be optimal.