This introductory chapter sets the stage for a project that critically examines justifications for permissible killing (pk), particularly in cases of abortion and euthanasia. It distinguishes de jure claims (about justification or rationality) from de facto claims (about truth), focusing exclusively on de jure defects in arguments supporting (pk). The concept of moral risk is introduced as an epistemically relevant factor in deciding how to act. Importantly, the chapter introduces the main argument to be defended in the book. (A) The arguments for (pk) suffer from serious de jure defects, and the arguments for ~(pk) suffer from trivial or much less serious de jure defects. (B) If the moral risk in being wrong in acting on (pk) is greater than the risk of being wrong in acting as if ~(pk), and the justification for (pk) suffers from greater de jure defects in relation to the justification for ~(pk), acting as if (pk) should not be done (C) The moral risk in being wrong in acting on (pk) is greater than the risk in being wrong in acting as if ~(pk). (D) Therefore, acting as if (pk) should not be done.