How many people can the good ship earth carry in comfort? The answer depends upon beliefs about optimal life-styles.If we want the planet to be a livable place, we need to promote social virtues, including trust and respect.
If the world's population had the productivity of the Swiss, the consumption habits of the Chinese, the egalitarian instincts of the Swedes, and the social discipline of the Japanese, then the planet could support many times its current population without privation for anyone. On the other hand, if the world's population had the productivity of Chad, the consumption habits of the United States, the egalitarian instincts of India, and the social discipline of Yugoslavia, then the planet could not support anywhere near its current numbers. Unfortunately most humans seem to fall in the America-India-Chad-Yugoslavia category.