You can arrive at this from many systems of values. If you value human happiness then more people even if a little less happy margins means more human happiness

You can arrive at this from many systems of values. If you value human happiness then more people even if a little less happy margins means more human happiness. If you value more innovation and progress then more people give you more opportunities for some innovative genius to come along. If you value human life as intrinsically valuable then more is straightforwardly better. Clearly I’m boiling down more complicated arguments to one sentence descriptions but I think the point is clear. Many human centered value systems can lead you to value more human life. If you have misanthropic values, then the opposite.