Should we aim to reduce the Earth population?

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Some say we would do well to aim to reduce the Earth population, in part to reduce the load on natural resources and ecosystems. Are they right? This question is about the desirability of the aim, not about the means to achieve it; specifically, it is not about whether the state should create laws that limit the number of children people can have. There are multiple ways to achieve the end and state coercion is only one of them.

Other formulations:

Should we aim to reduce the world population?
Should we reduce the world population?
Should we reduce the Earth population?

We should aim to reduce the Earth [human] population

Arguments for

Pro The larger the population of a highly technical civilization, the greater the rate at which irreplaceable raw materials are being mined and exhausted. Reducing the population size would extend the lifespan of such a civilization.
- Objection Rare raw materials such as those contained in solar panels could be recycled.
Pro A smaller population has a smaller impact on ecosystems, and is better in reducing elimination of the richness of biological form such as species. Impact on species is a serious concern, with massive species extinction taking place.
- Objection Earth has undergone many mass extinction events and the species alive today differ greatly from those a billion or 100 million years ago. This argument does not clarify why it would be a serious concern. For example, without such extinctions, humans likely would not be around.
Pro In the past 50 years, humans have managed to decimate the populations of wildlife all over the world by about 70%. This is clearly unsustainable and a direct result of growing the human population to such irresponsible, exaggerated levels. We need to reduce the global human population so that future generations of wildlife can even exist. If for no other reason, we should reduce the global population of humans so that future generations of humans can also co-exist with and appreciate wildlife and wild places, as we have been able to.
Pro This is relatively readily possible when considering modern contraception technologies and knowledge about factors that can shape people's reproductive behaviors such as education, later marriage, independence from offspring, contraception availability, and so on.

Arguments against

Con The problem is not how many people there are but rather how much resources do they consume. An increasing population is sustainable as long as it's usage of limited resources does not increase with it.
- Objection The average person's consumption has continuously increased. The majority of people do not want to decrease their consumption. If you want to make this argument, you need to get everyone to agree to reduce their consumption first.
- Objection More people = more consumption. There is not a single person on Earth who consumes zero resources. You cannot decouple consumption from population. The more humans there are, the more consumption there will be, and already, there are over eight billion humans and the overall consumption is massive enough as it is.
Con The more people on the Earth, the bigger the brain capacity to help solve problems and create abundance.
- Objection Even if this were true, is no rush for "solving problems" or creating abundance. From what we can see historically, over time the human condition has not improved. In spite of problems being solved and more abundance now than in the past, rates of depression, suicide, and general unhappiness are higher now than in the past. There will always be problems in the future, so it makes no difference how rapidly we solve them.
- Objection How many said-problems are a product of an unnecessarily large and complex human population?
- Objection No brain capacity can work around the limits of a physical system, and the Earth is one.
- Objection If the information processing problem solving capacity is so important and given how computing capability has been growing exponentially for decades, and given how human population has exploded in the 20th century, why is it that we have not seen more astounding feats in the first two decades of the 21st centurry? What was achieved does not approach such breakthroughs as antibiotics, jet airplanes, and travel to the Moon. The added value of brain capacity seems overestimated.
  - Objection Not all that is astounding is truly necessary. Antibiotics appeal to necessity, but what do we achieve from travelling to the Moon? Bragging rights? Food for interesting conversation? Perhaps some of the time used towards acquiring feats of potential transience like a zealous collection of trophies would be better turned towards mindful minimisation, lest there be no future for these feats to echo through.
Con The larger the population of happy people, the greater the total happiness of the greatest number.
- Objection Not only is the hypothetical happiness of non existent people not a moral concern, but the opposite argument could also be made; that the greater the number of people, the greater the total amount of misery.
- Objection Happiness cannot be quantitatively measured; it is a matter of qualitative assessment.
- Objection The total happiness of people is not the only morally significant concern. Biological heritage is also morally significant.
- Objection That may be rather temporary; the time dimension is key. It may well be that a steep rise to hights will be followed by a similar steep fall, whereas a much smaller population can be supportable for such a long time that, in some time frames, it will be larger than the steep-rise scenario.
Con All species populations in nature expand when they can. To do otherwise would be unnatural and in violation of laws of nature.
- Objection Species population behavior is a natural tendency, not a law of nature analogous to a law of physics. Human populations can and have been consciously regulated. True laws of nature cannot be violated.
Con This is not a concern. There is no such thing as a natural resource. The human resourcefulness is the greatest resource of them all.
- Objection No such thing as a natural resource? Ok, hold your breath forever. Oxygen is not a natural resource, right? You don't need it. Just stop breathing. No such thing as oxygen, or your need for it, since "there is no such thing as a natural resource". Also, stop consuming water in any form.
- Objection Clearly untrue. Send the arguer to the Antarctic to learn about the natural resource of a favorable climate; or to Sahara, Tibet or Siberia.
Con The Earth can sustain many more people: since the dire predictions in 1970ies, food has become much more abundant and death rates have fallen.
- Objection The Earth is only sustaining more people at the expense of ALL other species. There is no getting around this. In order for evermore humans to keep being created and added, more and more wildlife and wild places need to be completely destroyed. How worth living will life be for anyone if all the wild places are totally destroyed? If everything becomes man-made and there's no other species around, how enjoyable would life be? It would be like living in a nightmare.
- Objection Such temporary trends cannot be reliably extrapolated to indefinite future. Specific predictions of when limits are going to be hit may fail, but it does not change the fact of the existence of the limits. The Earth is a physical system, not a piece of magic. Exponential growth in a physical system is very unsustainable, due to the rapid and for humans unintuitive exponentiality.
  - Objection True, but the proposal is to reduce the population, not to stabilize it. The above argument is against growth of population, not specifically for reduction.
    - Objection Fair enough. However, even stable non-growing population may have a poor sustainability whereas a much smaller one would have much better sustainability, possibly meeting e.g. species-protection targets.
Con "The end of humanity will more likely come from collapsed birth rates than from climate change. The coming world population decline will not be reversed easily [...] It may well be necessary to ensure that global population numbers do not eventually fall below about seven billion if we are to avoid fading away."
- Objection That is far from obvious. In a situation of falling birth rates, there is going to be genetic variation driving differences in fertility and willingness to have children, and as a result of natural selection, genes that predispose to higher fertility and higher willingness to have children will start to dominate the gene pool in the middle run. Furthermore, once population declines by a huge amount, the ratio of population to sources easily available will greatly improve, creating conditions for reversal. The notion that once population starts falling, the trend is to be extrapolated indefinitely up to extinction is just another instance of foolish extrapolation from a single time series with no account for underlying forces and principles driving the series.