Yin/Yang. If you don't have both, you can't determine the other ever existed...no basis for comparison. Without a basis, it is all nothing. Your imagine becomes: "Imagine a world where everyone is nothing, a world where there is nothing, where nothing can ever happen." The last question, "Are we even human in that world?" is moot, with no comparative basis we probably don't exist. Equilibrium/balance is important. My Dad always used the "stall full of manure" aphorism. I'm the kid digging in the manure looking for the pony. I have no problem with both nature and nurture versions of happy/unhappy. Frankly, I think it is an aspect of our software/hardware which is not well understood at the moment. As an engineer, I know that the half-full/half-empty glass is at least twice as big as it needs to be, given a stable environment. If the environment is not stable, the glass may need to be resized or reconfigured to limit spillage and/or evaporation (within established parameters) due to unknown external factors.