Here is an excerpt from Candidate Scoring System about the value of population size:
Folk assumptions about ‘overpopulation’ are flawed and must be dropped, making it unclear whether our population growth is too high or too low for total human welfare (Greaves 2019, Ord 2014). 19% of economists agree that the economic benefits of an expanding world population outweigh the economic costs and 29% agree with provisos; 48% disagree (Fuller and Geide-Stevenson 2014). There are also non-human consequences of having a larger population. Humans eat meat, and animal agriculture and aquaculture generally involve negative welfare (Bogosian 2019). Much of the land we occupy would otherwise be occupied by wilderness, but it’s not clear if wilderness has net negative animal welfare (Plant 2016). However, this consideration is small in the long run since we can expect animal farming to eventually become more humane or outmoded.
From what we can see, the social cost of the pollution of a typical person, even in the West, seems small in comparison to a person’s whole life and impacts. Per our air pollution section, we can tentatively say that the social cost of carbon, including other impacts of air pollution besides climate change, is less than $200/ton. This is $3,200 per American per year. Meanwhile, American GDP per capita is $59,500. Thus, the average American seems to contribute far more to the world through labor than what they destroy via air pollution. There are other downsides of population growth, but they seem unlikely to be much worse than air pollution, and there are other upsides as well.
Changing population size now may also have a large effect on long-run fertility. Jones (2019) provides a model of economic growth with endogenous fertility and suggests that actual population growth may be either higher or lower than optimal, but in particular he shows that under certain assumptions insufficient fertility could lead to an indefinitely declining population with a corresponding stagnation of wealth and knowledge. This counts as an existential threat to humanity, albeit a relatively slow and mundane one that might be overturned by a Darwinian mechanism.
Of course, killing someone is worse than deciding not to give birth to someone.
Here is an excerpt from Candidate Scoring System about the value of population size:
Of course, killing someone is worse than deciding not to give birth to someone.