It seems most people think creating a life is a morally neutral thing to do while destroying one is terrible. This is apparently because prior to being alive and contingent on not being born, you can’t want to be alive, and nobody exists to accrue benefits or costs. For those who agree with these explanations, here’s a thought experiment.
The surprise cake thought experiment
You are sleeping dreamlessly. Your friends are eating a most delicious cake. They consider waking you and giving you a slice, before you all go back to sleep. They know you really like waking up in the night to eat delicious cakes with them and will have no trouble getting back to sleep. They are about to wake you when they realize that if they don’t give you the cake you you will be unconscious and thus unable to want to join them, or be helped or harmed. So they finish it themselves. When you awake the next day and are told how they almost wasted their cake on you, are you pleased they did not?
If not, one explanation is that you are a temporally extended creature who was awake and had preferences in the past, and that these things mean you currently have preferences. You still can’t accrue benefits or costs unless you get a bit more conscious, but it usually seems the concern is just whether there is an identity to whom the benefits and costs will apply. As an added benefit, this position would allow you to approve of resuscitating people who have collapsed.
To agree with this requires a notion of personal identity other than ‘collection of person-moments which I choose to define as me’, unless you would find the discretionary boundaries of such collections morally relevant enough to make murder into nothing at all. This kind of personal identity seems needed to make unconscious people who previously existed significantly different from those who have never existed.
It seems very unlikely to me that people have such identities. Nor do I see how it should matter if they did, but that’s another story. Perhaps those of you who think I should better defend my views on population ethics could tell me why I should change my mind on personal identity. These may or may not help.