It's not practical in the short term. Long term, I think we should build Dyson spheres or whatever else it takes to make as many happy people as possible.

What do you mean by every possible human that could exist having moral value? If you think it's bad to create them and then kill them, you're already assigning moral value. We already seem to agree on the idea that creating and then killing a person and not creating a person are morally comparable and not of equal value. The only question is which is better.