Anyone who calculates the cost of handling sewage and treats it as an avoidable cost errs grievously. Exactly this blunder is at the very heart of ecological analyses like Mr. Hawken's. More generally, much environmental fear results from faulty thinking. One crucial example is assuming that the quantities of resources are ultimately limited, and then deriving conservation policies from that assumption. The idea of nonfinite resources boggles the mind, of course, but the idea has withstood all scrutiny since it was first published in 1981.
Analysts stop there.
But one must also take into account the positive externalities, the most important of which is the new knowledge that people produce and for which they do not receive the full economic benefit. An example is Nobelist John Bardeen, co-inventor of the transistor. Indeed, the positive externalities of human beings generally outweigh the negative, as proven by the fact that humanity, by living longer and having more wealth, continues to progress in every material sense with every passing decade. Leaving out the positive externalities leads to a negative assessment of humanity's situation, when in fact everything is coming up roses.