This should spark some discussion - How many of us Humans can Earth sustain indefinitely?
Right now we're at 6.6 Billion and that's too many. Ask people in East Africa who are starving or, at best, eating in Oxfam Camps,if there are too many of us.
I've had some pretty heated debates (with College kids) in regard to this. To live in Utopia, a World In Balance, in Harmony With Nature, is probably against Human Nature, anyway. And, fewer babies born means a lesser chance of coming up with another Da Vinci, a Mozart, a Salk, a Schweitzer, an Eric Clapton. Less chance of another Hitler, too.
I go for 1.5 Billion, the population of Mother Earth in 1880, BTW.
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That's a tough question. For one thing, it would depend on whether or not the resource expenditure per unit of population would remain steady into the indefinite future. Even with a much reduced population, the resource usage could still conceivably rise to unsustainable levels.

The question whether there are too many of us, and I certainly think so, should perhaps be rephrased as:

"Who is in control ... sentient humans or our chromosomes?" Do we control the chromosomes or do they control us? Is a chicken just another way for an egg to make more eggs?

I would like to see anyone justify a human population over any arbitrary number ... 100,000,000 or 1,000,000,000 without resorting to theological imbecility such as "god told us to be fruitful and multiply" or the equally moronic "why not?"

It seems the primary purpose of increasing population these days is to provide more retail customers.

I think I've mentioned before that almost every difficulty we face is ultimately caused by the fact there are too many of us. That doesn't give any indication of how many is enough of course. Even the few hundred thousand Australian Aborigines altered Australia's ecology totally. Presumably it was the same for America's pre-European ecology. Certainly they exterminated the large herbivores along with a great deal of collateral damage.

That thought did occur to me, the fact that we, even in very small numbers, have managed to wipe out the Mammoth, the Passenger Pigeon, the Dodo, most of the indigenous birds of Hawai'i, almost all wild Orangutans and the Tasmanian Wolf. But, given the "Wisdom" that we possess today, I think 1 1/2 Billion could thrive without doing too much damage to the Environment. Too small a population and we would stagnate. Where's the future in a totally Agrarian Society? Oh, yeah, I can appreciate the "Harmony With Nature" logic, I grew up in the 60's. But eventually our Sun will either dim or go Supernova. Our species will need to find a way to "reach out", a la Gene Roddenbury, if it is to survive.

With a far smaller population we managed to produce the likes of Isaac Newton, J.S. Bach, Rembrandt, etc. A larger population may produce more retail customers and more cannon fodder but little else.

Were it not for leaders feeding animosity and hatred as a way to stay in power. Were it not for toady people who are willing to follow them into their insanity. We might well all be discussing this right now near Alpha Centauri.