You make some fairly large assumptions there OP (maybe deliberately). Have a look at your own question as it suggests some of your answers in itself... Who are 'we'? What is 'it'? The debates on what can be thought of as 'sustainable' or 'sustainability' remain to a large extent separate to the first two questions (at least in mainstream scientific/media/popular discourses) so I'll ignore them for the moment.
What I'm trying to get at is that your initial premises rely upon a nature/culture dichotomy (along with an essentialising conception of who 'we' are and how 'we' act, but lets leave that for now) which has been extensively critiqued, and if you look into it, it's fairly obvious why. Basically (though there is a significant degree of difference and approach in these critiques) part of what they are into is the rejection of views that position humans and culture distinct from, or in opposition to nature. Instead nature is understood to be inseparable from culture, both physically and conceptually.
To begin to understand how the non-human cannot be physically independent from 'us', (which is relatively easy to conceptualise- and obviously, we are significantly 'natural' in all senses genetic/biological/chemical...) consider the global effects of human actions that demonstrably alter the 'natural' world- eg radioactive fallout, anthropogenic climate change etc- witness environmentalist obituaries mourning “the end of nature” for precisely these reasons). Conceptually (which is a more complex point but might be summarised briefly), humans as organisms cannot be considered 'unnatural', conceptions of 'nature' can only be formed and interpreted through the social and cultural- conceptions of nature and society are always implicate in each other (the concept of nature relies upon socially constructed ideas of nature in order to know itself, and vice versa).
Thinking along these lines is a lot more interesting, and potentially more productive, than seeing nature as something other to us that we 'dominate' (as people have commented above) or lamenting the loss of an imaginary that never was (oh no, we're all so modern/urban/non-hunter-gathering, again commented above). There are loads of potential reasons why the standard discourse is dominated by these “narratives of loss”, paralleling the mythical fall from Eden, descent of modern man, and so on... that make these debates quite appealing to everyone who has a love of these type of stories (myself included).
IMO understanding things from a nature-culture perspective is significantly more promising when it comes to answering questions of sustainability. But I'll not go into that now.
Sorry for the long (and probably dull) answer, I'm on my own at lunch.