Eliezer, it seems you are just expressing the usual intuition against the the "repugnant conclusion", that as long as the universe has a lot more creatures than are on Earth now, having even more creatures can't be very important relative to each one's quality of life.

But in technical terms if you can talk about how much of a mind exists, and can promote more of one kind of mind relative to another, then you can talk about how much they all exist, and can want to promote more minds existing to a larger degree.