This is where we differ: a separate instance of a person is a separate person. I see no reason to attach special significance to unique experiences. Suppose you and an identical version of you happen to evolve separately on different worlds, make identical choices to travel on a spaceship to the same planet, and meet each other. Up until now your experiences have been identical. Are you okay with committing suicide as soon as you realize this identical person exists? Are you okay with Omega coming in one day and deciding to kill you and take all your belongings because he knows that you're going to spend the rest of your life having an identical experience to someone else in the multiverse?
Maybe your answers to all these questions are yes, but mine aren't. Society is filled with people who are mostly redundant. Do we really "need" Dude #3432 who grows up to be a hamburger flipper whose job eventually gets replaced by a robot? No. But morality isn't (shouldn't be) designed to protect some nebulous "society". It's designed to protect individual people.
This is especially true in the sort of post-singularity world where this sort of hypothetical even matters. If you have the technology to produce 1000 copies of a person, you probably don't "need" people to contribute to society in the first place. People's only inherent value is in their ability to enjoy life.
If I take your hypothetical in the sense I think you intend, then yes. In practice, I'd rather not, for the same reason I'd want to create copies of myself if only one existed to begin with.
I agree that the value of society is the value it provides to the people in it. However, I don't think we should try to maximize the minimum happiness of everyone in the world: that way lies madness. I'd rather create one additional top-quality work of great art or culture than save a thousand additional orphans from starvation.
(If the thousand orphans could be brought ...
(Apologies to RSS users: apparently there's no draft button, but only "publish" and "publish-and-go-back-to-the-edit-screen", misleadingly labeled.)
You have a button. If you press it, a happy, fulfilled person will be created in a sealed box, and then be painlessly garbage-collected fifteen minutes later. If asked, they would say that they're glad to have existed in spite of their mortality. Because they're sealed in a box, they will leave behind no bereaved friends or family. In short, this takes place in Magic Thought Experiment Land where externalities don't exist. Your choice is between creating a fifteen-minute-long happy life or not.
Do you push the button?
I suspect Eliezer would not, because it would increase the death-count of the universe by one. I would, because it would increase the life-count of the universe by fifteen minutes.
Actually, that's an oversimplification of my position. I actually believe that the important part of any algorithm is its output, additional copies matter not at all, the net utility of the existence of a group of entities-whose-existence-constitutes-utility is equal to the maximum of the individual utilities, and the (terminal) utility of the existence of a particular computation is bounded below at zero. I would submit a large number of copies of myself to slavery and/or torture to gain moderate benefits to my primary copy.
(What happens to the last copy of me, of course, does affect the question of "what computation occurs or not". I would subject N out of N+1 copies of myself to torture, but not N out of N. Also, I would hesitate to torture copies of other people, on the grounds that there's a conflict of interest and I can't trust myself to reason honestly. I might feel differently after I'd been using my own fork-slaves for a while.)
So the real value of pushing the button would be my warm fuzzies, which breaks the no-externalities assumption, so I'm indifferent.
But nevertheless, even knowing about the heat death of the universe, knowing that anyone born must inevitably die, I do not consider it immoral to create a person, even if we assume all else equal.