Much of Kagan's argument is derived from an interesting question posed by the ancient Greek philosopher Epicurus who wrote, "So death, the most terrifying of ills, is nothing to us, since so long as we exist, death is not with us; but when death comes, then we do not exist. It does not then concern either the living or the dead, since for the former it is not, and the latter are no more." In other words, non-existence cannot be said to be a bad thing in-and-of-itself. But Kagan aptly notes that this issue is much more complicated than that:
Moreover, there are a lot of merely possible people. How many? Well, very roughly, given the current generation of seven billion people, there are approximately three million billion billion billion different possible offspring—almost all of whom will never exist! If you go to three generations, you end up with more possible people than there are particles in the known universe, and almost none of those people get to be born.
If we are not prepared to say that that's a moral tragedy of unspeakable proportions, we could avoid this conclusion by going back to the existence requirement. But of course, if we do, then we're back with Epicurus' argument. We've really gotten ourselves into a philosophical pickle now, haven't we? If I accept the existence requirement, death isn't bad for me, which is really rather hard to believe. Alternatively, I can keep the claim that death is bad for me by giving up the existence requirement. But then I've got to say that it is a tragedy that Larry and the other untold billion billion billions are never born. And that seems just as unacceptable.