Advances in biotechnology have important applications to the core demographic concerns of human reproduction and longevity, raising a number of difficult ethical issues. In the debate over those issues, however, the voices of demographers and other social scientists are nearly silent. In the United States the dominant bioethical arguments currently heard come from a conservative political and ideological position, represented, for example, by the President's Council on Bioethics and in particular by its chairman, Leon Kass. A critical discussion of Kass's writings identifies the philosophical roots of that position and highlights its logic and limits. Kass's specific arguments on cloning can be challenged by applying them to an earlier and revolutionary technology, birth control; his views on death and dying would argue for curtailing investment in life-extending technology. Conservatism of this kind ignores social science perspectives and forecloses opportunities for social change.