Ecological: I haven't really seen anyone in this thread make this point. As much as humans like to pretend that we exist outside of the environment, we do not. We depend on functioning ecosystems just like any other biological entity. As Leopold said, had bluegrass not taken root in the cane-lands of Kentucky, we would not have settled that land when we did. Similarly in the West, if it was not for the snowpack of the Rockies, the Sierra Nevada, the Cascades, or the Wasatch Ranges, we would not be able to live on this side of the Rockies. We depend on functioning ecosystems for drinkable water, arable soil, irrigation in the dry season, and many, many other things. It is an inescapable fact that the more we expand as a species, the more damage we do to these ecosystems that we depend on. That isn't to say humanity should voluntarily go extinct, but mindfulness in our management and occupation of the land is necessary for the long-term survival of our, and many other species. Anyone who denies this is ignorant, willfully or incidentally.