Over population: My son has been examining “effective altruism” and considering how to make the most positive difference in the world. One idea I saw raised in such circles is how to maximize human happiness.
If (say, painlessly) killing people is bad because you deprive them of the rest of their life, (i.e. human life is a good thing), then are more people a good thing? If one believes or concludes this, there are broadly two scenarios:
1) we botch it all up through excessive population growth, consumption, environmental damage, etc and while I don’t believe all humans will become extinct, the survivors could end up stone-age, hunter-gatherer setting or something akin to low-level tribal agriculture. If so, an advanced civilization is a LOT harder to achieve the second time around when all the easy ores and oil have been extracted (landfills will be the prime source of raw materials). So you have a long-term population without agriculture, of 1-15 million or 100-200 million with primitive but widespread agriculture.
2) or we decide to control population at something sustainable – maybe that’s 10 billion if we get really renewable in our resource use, maybe it’s 5 billion. Or perhaps a forward-thinking generation realizes that their grandchildren will have better lives if they each have 3-5 grandchildren (total, from 8 grandparents) instead of 12-20, do that a few times and settle in at 2-3 billion.
Point being, even if you think more humans is a good thing, we need to not don’t crash everything and we can get past this potential pinch-point, then there could be a LOT more humans, living better lives, spread out in the centuries ahead.