While wealth and surplus energy are not exactly the same, they can be equated for the sake of a simple analogy to illustrate the danger and folly of employing surplus energy in dead-end practices that increase taxes on it.
Let's say that with X amount of wealth, a man can sustain his 100 kg body and 300 sq m home. Let's say he can also save Y dollars.
If the man spends the Y dollars on more food, which he regularly ingests, let's suppose he gains 10 kg. Those ten more kgs of cells require constant maintenance in the way of nutrition. Now, his Y dollars go to maintaining his 110 kg body.
Now, obviously supporting 10 kg doesn't cost $500, but let's suppose that the waste illustrated by spending money on extra body baggage is indicative of a general lifestyle of similar wastes and taxes that might, for example, increase the amount of stuff he has to move when he relocates from city to city but does not increase or improve much of anything else in his life. He spends Y on more food but also on more stuff. His 300 sq m home grows to 500 and more, increasing his heating and cooling bill, time needed to clean it, etc.
Focusing the analogy on the increase in weight, his breathing is slightly heavier and his heart has to work a bit more to take care of those extra 10 kg of cells. His lifespan has thus been slightly reduced, providing him less surplus time in which to acquire experiences and realize the self.
He used surplus wealth to increase his tax on his wealth. He increased the amount of nervous energy required to digest the extra food. He spent more time in food preparation than he might have otherwise. He required the farming and trucking industries to burn through more energy to supply him with his extra food. Perhaps he also failed to use a compost toilet and grow a garden, thus requiring a few extra visits of the septic tank cleaner. Indeed, the garden would have required an initial investment but would have saved money from his X dollars, further reducing the cost of his basic living.
Most people can understand the idea of extra body mass that serves no purpose in life. It is certainly true that in some times past or other places, weight might have been considered attractive. One's self-esteem might have benefited by excess body mass. But such incidental advantages do not erase the plain fact that extra poundage doesn't improve our person or lot in life. This is, to a large degree, also true of possessions. Indeed, with more poundage the brain to body mass ration only reduces, meaning more brain activity is required to manage more mass, limiting its energies in the face of its more refined faculties.
Now consider millions or even billions of human beings squandering surplus energy in this very manner. Easily millions of human beings are alive today spending surplus energy on practically supporting a second body. This second body doesn't have its own heart, brain, and spine, but comes in the form of fifty, 100, or even more excess kilograms.
A large share of surplus energy gleaned from fossil fuels was spent on increasing and maintaining our size and our numbers. We didn't stop to think if we could properly educate every child born or even provide access to medical facilities and expertise. Diseases -- many stemming from lack of hygiene, poor access to potable water, and poverty -- and starvation, homelessness and ignorance/superstition are still prevalent, only now more human beings are vulnerable and exposed to these curses of human life than ever before. On the flip side, other diseases are caused by too much sugar, too much harmful fats, and altogether too much food. With overpopulation came pollution levels that threaten to affect the gulf stream, raise sea levels, displace hundred of millions of human beings, adversely affect modern agriculture.
The single greatest challenge human beings face is to reduce their numbers consciously, avoiding the reduction that will invariably come through war, ecological devastation, scarcity of resources, disease/starvation/homelessness, and more than likely all of the above.
If the human race could progress, spiritually and scientifically, with half a billion people, it does not follow that it will progress faster with ten or twenty times that number. In fact, unless space and energy were in greater abundances than we currently possess, it more closely follows that five or ten billion people will jeopardize the progress of the human race. No one alive should be considered dispensable. Rather, we must consider that if a slimmer, more streamlined human race ideally numbered far less than seven billion, then procreation rates must reflect that ideal as best as possible.
Since growth rates decrease as education increases, we can surmise that the greater the amount of surplus energy directed toward education, the greater the reduction in taxes on surplus energy emerging from overpopulation.