Revulsion is not an argument; and some of yesterday’s abhorrences are today calmly accepted – not always for the better. In some crucial cases, however, repugnance is the emotional expression of deep wisdom, beyond reason’s power completely to articulate it. Can anyone really give an argument fully adequate to the horror that is father-daughter incest (even with consent), or bestiality, or the mutilation of a corpse, or the eating of human flesh, or the rape or murder of another human being? Would anybody’s failure to provide full rational justification for his revulsion at those practices make that revulsion ethically suspect? Not at all. On the contrary, we find suspect those who think they can easily rationalize away our horror, say, by trying to explain the enormity of incest with arguments about the genetic risks of inbreeding.
Leon R. Kass – Life, Liberty, and the Defense of Dignity: The Challenge for Bioethics p.150