I will now elucidate more carefully and clearly the main points of this thread and their consequences, particularly for environmentalism. (I apologize for the numbering, please take it as a kind of joke).
On presuppositions:
1) All language -- and all thought -- even scientific language, contains within it a set of presuppositions.
1.1) These presuppositions usually remain unconscious; in Zizekian terms they are the "unknown knowns": things that we don't even know that we know, but which have the force to influence our practices and our thinking.
1.1.1) The presuppositions (unknown knowns) can become conscious when a tension between presuppositions in different parts of our language begins to lead to contradictions. They can also become conscious through thinking about how we use language.
2) Even science, in investigating reality, can only do so within a framework of these presuppositions.
3) These presuppositions can be understood as part of a larger structure of practices, beliefs and fictions that give meaning to our experiences. The experience of reality is always partially structured by a "virtual" or "fictional" element, that provides meaning to our experiences.
On Nature:
1) The long history of the concept 'Nature,' means that it has had many uses and many meanings.
2) Science, in so far as it does not posit an "outside" to Nature, is both materialist, and monist. This is particularly evident post-Darwin, when human beings empirically became another species within the tree of life.
3) But particularly within the development of ecology, 'Nature,' even in the scientific sense, became overburdened with a traditional sense of eternal, cyclical, harmonious, balanced. (Predator-prey cycles; communities of species as supra-organisms that develop according to a fixed succession, etc).
3.1) Within climate science we find the glacial-interglacial cycle.
3.1.1) In all cases, extending the x-axis (time) shows that none of these cycles is eternal, and that catastrophes are a regular part of Nature.
4) Even within science, and in spite of what evolution teaches us, it is difficult to get away from the logic of oppositions: Nature gets opposed to culture, and natural gets opposed to anthropogenic (unnatural). (Nature, as a totalizing concept, is the concept which is capable of containing all opposites: it is everything. Even nothing (the void, death) is part of Nature).
4.1) This is partly for pragmatic reasons; the desire to distinguish between what would have happened (say in the climate) if humans had not existed, or had behaved differently. This is often important for shaping policy.
4.1.1) This way of thinking is prevalent in the environmental movement, where it lends itself to a kind of romanticism expressed in the concept of 'wilderness': that which is "untouched by man."
While I appreciate George Monbiot's work, his profile on Twitter is a perfect example of this sort attitude. He quotes Lord Byron (the British Romantic poet) who wrote: “I love not man the less, but Nature more.”
So we find in one of the most outspoken journalists on climate change a repetition of the movement that separates human beings from nature, setting Nature up as the "ideal."
We also find this in Bill McKibben in the title of his book "The End of Nature."
4.1.1.1) We could read the title "The End of Nature" in a different way
5) The End of Nature: The collapse of our old concept of Nature as something separate from us, which is harmonious, reliable, without catastrophe (until humans -- or some subset of humans -- ruin everything).
This is the kind of "End of Nature" that I arrive at when I suggest that by renaturalizing human beings (and just for Nanning and Tim's sake, I'll specify: "the very worst of human beings"), all cultures, all political and economic decisions, all human blunders, we denaturalize Nature.
5.1) We do not denaturalize Nature in a literal sense (which would make no sense): we liberate the concept from a "fiction" that has given it a specific meaning (and force). It no longer means what it did before. If it is still Mother Nature, we can quote Zizek and say, "Mother Nature is a dirty bitch."
5.1.1) This does not mean that we liberate the concept from fiction all together.
As a consequence the challenge becomes how to build a new environmental ethics, not built on a fiction that prevents us from seeing large parts of nature (which demands that we sever certain parts of human behaviour from nature, and understand them as something alien).
Why is this important? I hold that environmentalism in the current form (which depends on this mythology, this fiction with its dualistic presuppositions) is ultimately ineffective. It is based upon an idealistic move, and -- as Nietzsche argues -- idealism contains within it already the seeds of nihilism, is a form of nihilism, or not seeing things as they are.
More later...