But U(3) = U(2) doesn't reflect what I was suggesting. There's nothing wrong with assuming U(3) ≥ U(1). You can care about A even though you think that it would have been better if they hadn't been born. You're right, though, about the conclusion that it's difficult to be unconcerned with a person's existence. Cases of true indifference about a person's birth will be rare.

Personally, I can imagine a world with arbitrarily happy people and it doesn't feel better to me than a world where those people are never been born; and this doesn't feel inconsistent. And as long as the utility I can derive from people's happiness is bounded, it isn't.