I believe you start in the wrong place by assuming that our species is a "we"; it isn't. Our species is a population of competing genomes. We will not share if we can conquer. That is why scarcity that cannot be ended by cooperation leads to aggression. The Israelis on a kibbutz work together to create growth. The Nazis after WWI saw no such hope after Versailles and so took what they "needed."

Growth is the panacea, because growth is the alternative to war. Capitalism implements the strategy of seeking growth. Where there is no capitalism, there is competition among classes, castes, blocs, etc., and that competition is as violent as the eventual winners need it to be. That is how we roll. Any scheme that proposes that all humans work together to make do with less than the winners could win in a war just doesn't reflect the reality of homo sapiens and natural selection. (I am not a "social Darwinist, but I am an evolutionary Darwinist, and I believe natural selection favors growth over war and war over sharing.)

The paperclip maximizer is not a useful metaphor because the machine is not a subset of humainity. There is no reason to believe that our equivalent of the "killer bees" won't in fact eliminate enough people to make renewable energy sufficient. The only solution to scarcity is to match population growth to economic growth. If we stop economic growth, we must stop population growth, a result best accomplished, in Darwiniian terms, not by everyone abstaining from reproduction, but by winners killing losers and breeding for all they're worth. The USA appears ready to surrender Franklin's "republic if you can keep it" over the price of oil. Good luck with world cooperation.

Finally, the idea that scarcity is "artificial" won't support the weight put on it. Is the scarcity in the non-capitalist world, where people are starving for food and water artificial? Only in the sense that corruption makes it impossible for growth to happen. But the leftist notion that capitalism is to blame for the scarcity that governs human history is just silly. Scarcity existed before capitalism, and it will exist after it, because we breed until it describes that's available. (Anyway, relying on someone's the "definition" of "economics" as a premise for reasoning about the real world is really a suspect approach.)