system
Given the following post, respond as if you're commenting on Reddit:
human
If humanity isn't going to develop a fully sustainable method of living, then it must greatly limit and lower it population. CMV.

Having studied in depth the effects of our population level on the environment, the dangers of having too large populations on a population ecology and genetic level with the pollution of the gene pool etc and the dangers of having the whole planet living the way that most developed countries do and the oncoming climatic and environmental problems (not ignoring of course the destruction and fragmentation of ecosystems, great losses of biodiversity, deterioration of many of our agricultural land through soil erosion and loss of soil nutrients and many others) my conclusion has been that if humanity does not seriously change the way it lives, massive decreases in the current level of the human population is necessary in insuring the long term survival of our species. CMV 

* Leaving in the original badly written post, but adding a clarification. Many of this systems on this planet a changing into an undesired, for us humans, state. Most of the damages are anthropogenic, or at least can be somehow blamed on humanities activities. My point is that if we do not change our methods of living as a whole, and we decide to stick to them, the only viable way is by greatly limiting the amount of people that do it. Thus, lower the population. That, or keep it as it is, while dramatically changing nearly every single aspect of the way we live. It is not the numbers of humans that count, but the amount of humans living in a fashion similar to us westerners..
gpt
Thomas Malthus thought the same thing in 1798.

He wrote his "Essay on the Principle of Population" which theorized that, since population grows geometrically (2, 4, 8, 16, 32, 64, 128, etc.) and since agricultural land was limited (and, at best, could grow arithmetically, or 2, 4, 6, 8, 10, etc.) we would have to severely limit population in order for the developed world to not literally starve to death.

But, with greater need comes greater innovation. People tend to naturally limit population growth (lower birth rates in the developed world) and people have come up with far more efficient ways of farming. Malthus thought that, even with its colonies, the island of Britain couldn't fit as many people as are in London alone today.

In regions with good soil, modern farming technology can have just a few places be breadbaskets of the world, operating in a relatively small area. The Soviet Union was the largest country the world has known, and Belarus (a small part of it) supplied food for most of the union. North and South America, with greater preservation and transportation technologies, could probably feed the world on their own.

Technology rises to meet the needs of a population, so this shouldn't be much of a problem. With current technology, we could probably supply around 10 billion, easily, and we keep developing every day.