Of course this still leaves the philosophical issue: What if Malthus were right? Suppose we could snap our fingers and increase world population to 50 billion at the cost of a drastic reduction in average living standards. Does the aggregate increase in human life outweigh the decline in the average? Derek Parfit famously argued that it did, but it goes against a lot of people’s intuitions.
I want to say no, my actual, comfortable, modern life is worth more than 7 or 8 potential, difficult, but ultimately worthwhile lives, but I find it difficult.
Imagine you are going to die tomorrow (so the result doesn’t effect you), and you can, without turmoil or increasing the biological damage done, add 40bn or so souls to the planet earth. Would you, at the cost of making everyone radically poorer?