I agree overpopulation is a myth. Can anyone say the world would be better off without some segment of the population? Even if you cut out all the slum residents around the world, that would still harm the local economy because slum resident contribute immensely to the urban economy as street sweepers, rickshaw pullers, house cleaners, cooks, etc.
I don't think anyone proposed to cut down any particular segment of population. It's a general observation that you will run into problems if you have too many people. No one ever says anything about eliminating "street sweepers".
Overpopulation alarmists also don't understand global economics. They don't understand economies of scale or specialization of labor. They think if Earth's population were reduced 80% to 400 million, then it would be the richest, most prosperous people. But by the logic that fewer people=richer people, if you cut the population down to two, would you have two trillionares? No, you'd have two hunter-gatherers, dirt poor, struggling to survive.
I think you are the one who is ignoring the general principles of economics. It's all about supply and demand. When you have more people and supply cannot keep up, demand will be up. price will be high. This is especially true with important stuff like food and energy. This leads to inflation and so on and so forth... What happens when people cannot get what they want? They start wars...
The macroeconomics dictates that the supply-demand curve will simply shift together while the entire economy will maintain its balance and equilibrium when the population shifts since both supply and demand drop together with a population shift. Yes, you have fewer demands, but you also have less capability to produce with lower population. So both supply and demand go together. So the fraction of wealthy vs. poor will not change when you change the population. This is, of course, under the assumption that we still have a decent population base. If we run into a problem of having only 2 people left on the planet, the last thing one worries about would be who is wealthy and who is poor...
What about the finite resources fear? First of all, energy is unlimited and replenishable when considering the Sun's radiation. Then there is the future of fusion energy which will utilize hydrogen and helium, the two most common elements in the universe.
Infinite energy is important because it makes recycling economically feasible and extends the life of existing materials.
Second, global food production has outpaced global population growth for the last 150 years. Famines around the world such as China's Great Leap Forward in 1958-1961 were due to bad human management or distribution, not an absolute lack of food.
Infinite energy is, of course, the goal. However, one cannot simply plan/strategize based on a hope that no one knows when/if it can be realized. In the mean time, we have to form plans and make predictions based on what we have at hands.
Unlimited resource is a myth. How can you say that when it is clear that available land for food and other resources is inversely correlated with population increase? More people, less land, less trees, less water. Just look at the Shaanxi and Shanxi, you will know what I'm talking about. A mere 5-6 centuries ago, that area of China was covered with forests. People cut down trees to build palaces and now it's nothing but yellow dirt. The Mayans had to abandon their homes because of lack of resources. The people on the Easter island went almost extinct because they lost all their resources. If it could happen on a smaller scale, it could happen to the entire planet.
Second, global food production has outpaced global population growth for the last 150 years. Famines around the world such as China's Great Leap Forward in 1958-1961 were due to bad human management or distribution, not an absolute lack of food.
This is wishful thinking at best. Human mistakes get magnified when there is a natural disaster. There was a massive drought in China between 1958-1961 in central China. It was magnified through human mistakes. You cannot rule out natural disasters and same goes with human mistakes. So if our food production is only barely enough to feed the people on this planet, any large scale natural disaster will push it over the limit and push the entire planet into a disaster.
IMHO, there is a population limit. And it is impossible to pass that limit. Either we correct it ourselves, or mother nature will take care of it for us in the form of famine, plague, war, etc.