As I defined it on my other site, this is the economic doctrine which holds that the more wealth is created, the poorer we will all be. It underlies, as a quasi-moral sentiment, all variants of Leftism.
To call it pessimistic is to miss the point: it is a misanthropic anti-humanism. A great many of the exponents seem uncomfortable that humans exist at all. They seem to be quite willing to kill the human race to save the planet. This is the necessary outcome of removing notions of qualitative superiority from the table.
The reality is that I can think better than my dog. I can think much better than plants. I have a right to exist, and a duty to exist. Everything that is, endures. This principle reality necessarily reaches into an understanding of reality, and the nature of life.
People that think we are machines made out of meat have no way of differentiating us from machines made from fewer parts. As William James pointed out, all questions of action and philosophy necessarily proceed from a fundamental myth–taken in the sense of a gestalt that involves more than just your brain, and that is a whole–of reality.