Q : You said that "either miserable people can be sacrificed so happy people can exist, or potential happy people can be sacrificed so suffering people don't have to exist," doesn't that mean that either way it's unfair? If that's the case why not stick with the status quo?
A : The reason this argument doesn't work is because even though it's unfair in both situations it's not equally unfair. Potential happy people won't miss what they haven't been alive to experience, but suffering people will suffer from existing. Therefore, it makes more sense prioritize suffering rather than happiness.