I know this is off topic, but: There are too many of us. If we can't override our survival instinct to multiply (and consume) uncontrollably, then we are at risk of making ourselves extinct. Then there will be none of us.
Long term accumulating issues that become unrecoverable past a tipping point could be a source of extinction (e.g. extreme worst case climate change). Here, yes, exponential growth could hasten extinction in a world where people weren't trying to stop the catastrophe, but...
1. Empirically, we're not on an exponential curve or anything close to it. Many developed countries would be in population decline without immigration.
2. Generally, the best solution to problems of efficiency or long term threats is improved technology, not reducing population. In the concrete case of climate change, cutting emissions per capita by >50% is both achievable and clearly superior to the Thanos approach.
3. More people can produce a more interesting universe to live in. Imagine a solar system colonized with 10 trillion humans: provided we build the requisite efficient infrastructure to unfetter human creativity, we would have the capacity to produce over a thousand times as many isekai animes.
And I appreciate your optimism. Not sure if it's been done much, but more honest analysis - that isn't biased by human emotions like hope of survival - on the history of the natural world and all evolution across all organisms from the beginning until now, analysing which behaviours result in which outcomes in terms of species extinction and resources sustainability, would be appreciated. No one wants to hear bad news, but we have to take its possibility seriously.
The U.S. alone wastes about 141 trillion calories worth of food. It comes out to around 1250 calories per capita.
Feeding the world is a logistics problem right now, not a production problem. And we also have the space for all 7 billion humans with room to spare. I think right now, there's enough for everybody to have about 4 acres.
It's seems preferable to have a lower stable population where everyone has a very high standard of living and a low aggregate environmental impact.
A flat cap of two children per person would halt and slowly reduce the population without killing anyone or being unfair to specific groups.
Once we define the threshold of high standard of living, we can optimize for it. This is literally when we say "nearly nobody can live as opulent as this" and can condemn waste. Feel free to pick say 90th percentile or something.
If there was one thing that we could do to increase sustainability, it would be to Increase quality of life as fast as possible
The eugenics thing is doubtful; what exactly is the mechanism that ties eugenics to population controls? There are myriad ethical ways to control population. For example, just make all countries advanced and the people will choose to have fewer children, as is happening already now.
Granted, there's much more to sustaining humans than just food, but come on let's apply some engineering to the problem first before giving up.
There's another, better reference but it escapes me at the moment- something calculating that with various engineering techniques applied to the planet, 100 billion people shouldn't be an issue.
Edit: Wow has it been 15-17 years already? Good seeing you.
[1] Agricultural productivity in relation to population, 1963