A few years ago, Richard Doerflinger, a pro-life Roman Catholic intellectual with decades of experience in the trenches of America's culture wars, was invited to debate the moral and legal status of the human embryo before a large class of Harvard undergraduates. During the course of the discussion, Doerflinger's Harvard faculty interlocutor drew a timeline of human biological development on the blackboard: conception, implantation, brain waves, viability, birth and so forth. His challenge to Doerflinger was to defend, in a nonarbitrary way and without reference to religious principles, the notion that society should recognize moral value and legal rights at any particular point along that line. If here, why here? If there, why there?
After the class, as the conversation continued with a few students and the professor, Doerflinger took a piece of chalk and extended the timeline to the end of the...