For your consideration: I propose that no one really believes that full human personhood begins at conception. If they did they would be morally obligated to attempt to save the life of every fertilized egg, which no one does. Natural abortions, or miscarriages, happen all the time, yet there is no movement to attempt to save the life of every miscarriage. Also, if a fertilized egg were a full person, it would have all the rights of a full person which would also include all inheritance and legal rights of a person. No one fights for this. Why not? Because the belief is socially religious and surface with no committed depth. Also, people actually realize the revolutionary implications for society if every fertilized egg were recognized to have the full rights of personhood, and they don't really want that.