The textbook has answers. In this case, “kin selection”. Of course some people sacrifice themselves for non-kin (Rachel Corrie, for example(*)) but these are the rare cases of an evolutionary strategy gone berserk.
Again, all questionable, of course, but IMHO fairly essential to reductionism of all sorts (even if not biological) seeking a scientific patina: people revolt not because of [mushy] moral reasons, but because of rational self-interest, biological preservation, revolutionary consciousness, so on.
Insofar as these things must be reduced, I [personally] much prefer the [poetic] notion that such rebellion arises from an inner discontent, from a psychological or subconscious awareness of alienation. And indeed such alienation could be from nature or a natural state. The counterpoint is simply that optimal [alternative] configurations of reality may be found or felt with or without an examination of or yearning for nature. To put it another way, it is quite possible that nature is sufficient, but not necessary [to explain and remedy our ‘condition’].
Again, I see and appreciate your essential point. It is [to me] not problematic, except in a strictly formal sense, to draw a line between nature as-is and nature as reconfigured by human natures (humans being the creatures who can overcome the limits imposed by “nature" on the exploitation and manipulation of, well, “nature”).
—ravi
(*) my own modest effort in memory of Rachel Corrie is here: http://l.ravi.be/kbxgSJ.