Because you say so? Since 1960 the planet's grain harvest has tripled while the population has doubled. Has world hunger been eliminated? No, much of the grain is used to feed animals (or make fuel). Who eats most of the animals?
Furthermore, the green revolution was made possible by cheap petroleum and plentiful water. Both of these resources have been used as though they are limitless. Returning to the island analogy; the island earth does not have infinite resources. One generation's freedom can mean the next generation's poverty and adversity.
Pakistan News Sept 25
Just a few decades ago, Pakistan was considered to have a profusion of quality water, but a recent World Bank report declared that Pakistan is among the 17 countries that were currently facing a water shortage, Dr Choudhary said.
And in India:
In the past two decades, the groundwater table in Punjab has been falling at the rate of 25-30 centimetres (cm) a year, says N S Pasricha of the soil engineering department, PAU. According to a study by Hira, out of the state’s area of 5.03 million hectares (ha), 4.32 million ha has a falling water problem. Going by the statistics of the state groundwater department, the area where the water depth has gone below 10 m increased from three per cent in 1973 to 25 per cent in 1990 and 46 per cent by 1994. If the water table goes below 15 m, the tubewells will stop functioning.
The State of the World Report, 1998, published by the Washington-based Worldwatch Institute, says the gap between water use and sustainable yield of the aquifer is so high that the aquifer under Punjab could be depleted by the year 2025.
The primary reason for extraction of groundwater is for agricultural purposes, particularly for water-intensive crops such as wheat and rice.
USA Today March 2008
AS THE WORLD'S DEMAND FOR WATER has tripled over the last half-century and, as the need for hydroelectric power has grown even faster, dams and diversions of river water have drained many rivers dry. As water tables fail, the springs that feed rivers also go dry, reducing flows. Numerous nations are overpumping aquifers as they struggle to satisfy growing water needs, including each of the big three grain producers--China, India, and the U.S. More than half of the world's people live in countries where water tables are falling.
There are two types of aquifers: replenishable and nonreplenishable (or fossil). The shallow aquifer under the North China Plain and most found in India are replenishable. When these are depleted, the maximum rate of pumping automatically is reduced to the rate of recharge. For the fossil variety, such as the vast U.S. Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquifer, depletion brings pumping to an end. Farmers who lose their irrigation water have the option of returning to lower-yield dryland farming--if rainfall permits. In more arid regions, however, such the Middle East or America's Southwest, the loss of irrigation water means the end of agriculture.
Underlying most wars and conflicts, there is a struggle for resources.
What I am trying to convey is that the more dense the population, the greater the need for rules. This is true in a family with many kids, It is true in a densely populated city, it is true of a densely populated planet.
Of course, most civilizations collapse because people are unwilling to plan for the long term if it means cutting back in the present.