False premise. There is no such thing as "over consumption". I continue to wait for someone in this thread to explain the universal rule of consumption that should be applied to all humans on the planet. What arrogant equation have you dug up that determines how much people are allowed to consume and how many kids they are allowed to have?
I don't think anyone has suggested that there should be a universal rule of consumption. Rather, we have suggested that the current rate of consumption is high enough that it is not supportable. Use up all your top soil, and farming becomes much more difficult. Cut down a forest, and you no longer have a valuable resource - not just a source of wood, but also a repository of ecological diversity, a place that helps create climatic stability, a natural water purification system, a gaurd against errosion, etc.
Of course, in the process of using those natural resources, we also gain something. Wood for building or paper, perhaps more efficient food production in the short term. etc.
Consumption by individuals creates demand for consumption of natural resources by those supplying products and services to individuals.
By over consumption all that we (or at least I) mean is when the rate of consumption by individuals is higher than the natural environment can sustain.
By this logic we should all limit our consumption. But clearly some consume more for less gain than others, and thus their consumption can stand to be limited more as well.
Limiting consumption is a very complicated issue. It may require cultural changes. Some may feel that those changes are unwarrented or impossible.
The easter islanders may have felt similarly about the over consumption of trees for building Moai. They may have felt that they had as much a "need" for this religious and social construction as anyone today does for their cell-phones and dvd players. Nevertheless, their children were impoverished because of their overconsumption.