Our relations have reached a point at which the entire planet is but one society.

Maybe, maybe not. What if we killed off all the people who don't look like us? Then, our species greatly reduced use of planet-destroying and depleting resources would pose not threat to us survivors. I am not a Randian objectivist, but, still, one must deal with the possibility that our species is more likely to cull itself than share among itself. Sharing is fine for plus-sum opportunities, but nature doesn't really favor it when sharing means living less well for everyone.