As gate discussed, this world, like any closed system, is self-balancing. There is no argument about that. Fundamentally, the world as a system only has sunlight as input, and the output is limited to heat and other various forms of radiation. If you want to get picky, the occasional ball of space junk we decide to catapult can be listed as 'output', too.
The part of gate's logic (as well as Jaez's points in the original write up) that troubles me is that humans have acquired the ability to destroy much faster than natural forces are able to create. Furthermore, as much as there are very smart people in every field, the average person is ignorant (and often indifferent) to the effects of their actions. Because of this, we as humans may not follow the same self-balancing pattern of other historical predators, and we risk bringing both ourselves and the planet we are on to a lifeless ball of ash.
I will admit: throughout the course of the evolution of life so far, every predator has either found a balance with the surrounding life around them. Alternatively, they consumed all they could, starved themselves out, and were wiped into extinction. From there, the remaining ecosystem replenishes itself and continues as usual.
The trouble with humans now is that we don't consume just a small fraction of the ecosystem. Our 'every part of the buffalo' approach to consumption means that if we don't find a balance with the surrounding ecosystem, nearly everything is being taken down with us. We are not simply wolves who have taken all the deer before starving. We have taken the deer, trees, and every other animal, small and large. What is left to recover when we succumb to our own stupidity? These troubling questions lead me to believe we only have one chance at this self-balancing model. We must take it seriously.
Humans are plagued with a sense of entitlement as well as a natural hubris. We think we deserve the best. More importantly, we think we are entitled to it. "I NEED a car", "Pass the steak (I want a third helping)", "Think of the children!". It is this mix of natural human consumption mixed with the feeling we are entitled to consume more (and spawn more children, which will require even more consumption) that will be our downfall. In the end, there are only so many acres of land to find food on. hramyaegr touched on this point earlier. Even when there is not enough land to feed everybody (which there very well may not be right now), our sense of entitlement will keep us breeding and demanding more. The trouble is, nature works on it's own time. We can't bully it. All that's left then is for us to grow up, or pick nature to the bone, effectively destroying us all.
I fear for our ability to grow up as a collective society and act responsibly. I really, really do.