Regarding the recipients of transplantation, there is some primordial revulsion over confusion of personal identity, implicit in the thought of walking around with someone else's liver or heart. To be sure, for most recipients, life with mixed identity is vastly preferable to the alternative, and the trade is easily accepted. Also, the alien additions are tucked safely inside, hidden from sight. Yet transplantation as such — especially of vital organs — troubles the easygoing presumption of self-in-body, and ceases to do so only if one comes to accept a strict person-body dualism or adopts, against the testimony of one's own lived experience, the proposition that a person is or lives only in his brain-and-or-mind. Even the silent body speaks up to oppose transplantation, in the name of integrity, selfhood, and identity: its immune system, which protects the body against all foreign intruders, naturally rejects tissues and organs transplanted from another body.Eugene Volokh responds,
This is, I think, a variant of the Is-Ought problem, with a dollop of coming to believe one's own metaphors. A procedure is physically dangerous; therefore it ought to be seen as morally troubling. A procedure is revolting to many people (as are prostate exams, I suppose, or changing diapers); therefore we ought to assume that it's presumptively improper. If we'd consistently adopted such an approach, in what century would medicine be stranded?The Kass quote, incidentally, comes from Life, Liberty, and the Defense of Dignity, page 186.
UPDATE: My favorite comment so far, from commenter Dave Griffith: "As someone with an auto-immune problem, I presumably am passing histological moral judgements against myself. I'll admit it's probably a fair cop in my case, but that's beside the point."