Once I wrote:
In fact trees and shrubs are a part of us, they are simply at a greater distance from our body than hands or feet, so it is possible to think that they don't feel pain, that chopping away our branches and trunks doesn't cause us serious injury. But we cannot live without trees. The fewer trees there are, the less we live. In reality we are chopping up and cutting down parts from our own body, we are burning and poisoning ourselves. Instead of the forest new human beings can be born, but they are disabled people, people without branches, without roots, without trees, without Amazonia, without Borneo, without Ruwenzori.
(Ice and Heather, in: Evening Brings Everything Back, Bloodaxe Books 2004)
Nearly nothing to add to this. We are a part of Nature, Nature is a part of us. Makes no sense to discuss why we must protect it. As if we discuss whether we should protect our head, our teeth, our liver...