I thought he asked a pointed question that got right to the crux of the matter. I did not think for one second that he was advocating killing retarded people or classifying them as non-human.

What I thought he was doing was taking a highly abstract conversation and expressing it in real terms. We're taking words that have reasonably firm meanings and we're thinking of different situations and asking ourselves - do the terms still make sense.

What is intelligence? What is sentience? What is human? What is a human being? To what extent do our answers to these questions reflect our collective moral sense?