Overpopulation alarmists often wring their hands and fret over some ill-defined number known as the planet's "carrying capacity." This is maximum number of human beings that the resources of Earth are theoretically capable of sustaining at one time, and represents the practical upper limit of population. No one knows for sure what this number is, but we can be fairly certain that human beings have been able to revise it upward.
If human beings were solely limited to hunting and gathering for subsistence, the planet likely could not support more than a few hundred million people at a time, and familne would probalby be a yearly occurrence somewhere or other. Because humans developed agriculture, irrigation systems, chemistry, etc., it is safe to say that right now there are many more humans alive than the planet could provide for were we limited only to harvesting the wild. A more immediate example is also suggested by the ability of human beings to live for periods underwater and in outerspace, environments that are fatal to mankind in the absence of technology.
It is reasonable then to wonder if the principle involved, i.e. that technological progress has expanded the native ability of the planet to support humanity, is applicable generally. Has the progress that civilization has enabled led mankind to be so dependent on this progress that disaster will result in its absence? We can see many areas where civilization had led to possibilities that were unavailable to our more feral ancestors. We have made progress, not only in the areas of technology, but in our attitudes toward others. We have become more refined in our views on exploitation of others, crime and punishment, charity, and human rights. Surely the progress made by civilization (including western civilization with the Renaissance, Enlightenment, and notions of individual liberty) have resulted in improvements in the human condition, which would suffer greatly were that progress to be abandoned. Just as the development of agriculture allowed the human race to expand beyond the limits imposed by nature, political philosophy that recognized and respected the value of individual liberty allowed mankind to live leves beyond struggles for survival.
The reason this is an issue is because there are those who openly disdain western civilization, and who would reject the centuries of human progress achieved through experience, struggle and a significant amount of bloodshed. They prefer that the mass of men live lives under the restraint of dubious theories.
Not everyone is pleased with the technological accomplishments of mankind. There are some environmental purists who pine for a planet unmarred by man's hand, famine and misery be damned. Likewise there are those zealots that are hostile to individual liberty, because it conflicts with idealilzed notions of humanity as a uniform, conforming hive.
If mankind were to turn away from agriculture, the planet would revert to it natural carrying capacity, necessitationg a compensatory die-off of billions. If mankind were to turn away from the advances that arise from individual rights and individual liberty, the results would be no less disastrous.