"But why is it good and necessary for the earth to have more than 4 million people on it? Sure, from the perspective of people in industrial societies, we think larger human populations are better, but that moral/ethical standard is a product of social life in an industrial society. Societies with large populations are not "better" than societies with small populations, unless you arbitrarily use the standards of industrial societies to decide what's better."
Why is it necessary for the earth to have more than four million people on it? Itis not necessary, but it is marvellous. People are marvellous, and the more of them, the better. Just think of it this way, would the world be any worse off if Miles, or Andie, or Sean or Patrick or Yoshie, or Wojtek oe me were not on it? Probably not. But I am glad that every one of them is, and all the other six billion, too. Is the world better off for having Michaelangelo or Chin Peng, De Chirico or Ibn Battuta, Martin Heidegger or Heraclitus, Ambrose Bierce or Jacques Verges, Brunel or Brunolesschi?
There is nothing arbitrary about using the standards of industrial society, when those standards put a greater value on human life than the standards of hunter-gatherer society. That is why industrial society is superior to hunter-gatherer society. More than that, that is why it is possible to see the limitations of industrial society: it does not put enough value on human life.