We were hunter-gatherers for most of our early history. For millions of years, human populations remained low and could be sustained by living off the land. Then, about 100 centuries ago (10,000 years before present, just at the end of the last major ice age), humans discovered agriculture, which allowed us to produce much more food. As a result of increased food availability, human populations grew much higher. With the advent of agriculture and more food, humans could live in much more densely packed villages and cities. This, coupled with the invention of money, allowed manipulative individuals to acquire greater power over others by controlling resources such as land, food, water, and shelter. Vast areas were deforested to grow crops to feed the burgeoning human populations. People spread out to new lands and continents taming the wilderness until we encircled the entire globe.
Unlimited cheap clean energy, such as that so ardently hoped for in the concept of cold fusion, would actually be one of the worst things that could possibly befall humans. Such energy would enable well-meaning but uninformed massive energy consumption and habitat destruction (i.e., mountains would be levelled, massive water canals would be dug, ocean water distilled, water would be pumped and deserts turned into green fields of crops). Heat dissipation would of course set limits, for when more heat is produced than can be dissipated, the resulting thermal pollution would quickly warm the atmosphere and the oceans to the point that all life is threatened, perhaps the ultimate ecocatastrophe.