When is killing morally objectionable? The answer is especially controversial in certain special cases. For example, it is not clear that abortion, which involves killing a human being during early development, is objectionable, or, if it is objectionable, how wrong it is. In some cases, killing ourselves, or helping others to kill themselves, may also be unobjectionable, or at least far less objectionable than killing people who want to live. In later chapters in this part of the book I will examine these special cases: suicide and euthanasia in chapter 8, and abortion in chapter 9.
Despite controversies arising in special cases, it is clear that, ordinarily, it is terribly wrong to kill people, and it is likely that killing other sorts of creatures will be objectionable, to some degree, for related reasons. In this chapter I will put aside the special cases and ask why killing is ordinarily wrong.
To make the inquiry manageable, I will need to refine the question a bit. Whether an action is wrong is a complicated matter. The presence of some features can strongly suggest that the action is wrong. But other features can strongly suggest that the action is not wrong. Whether the action is wrong all things considered depends on all such features. In other words, an action can have a wrong-making feature even though, all things considered, it is not wrong. When it has a wrong-making feature, it is prima facie wrong. Instead of asking why killing is wrong, I will ask what features make killing prima facie wrong.