We inherited an earth stacked with tons of low entropy, and a sun providing us with 4 billion years of low entropy in reserve before we need to leave Earth.
Carefully managed, this is not locally zero sum, and we can all benefit. Unfortunately, that doesn't satisfy some people, and they use their resources to disproportionately acquire even more resources until the peasants are left fighting for scrap.
The amount of sunlight is not the zero-sum to worry about. For each of us individually the number of hours that we will spend breathing is limited. Life is therefore absolutely zero-sum, no matter what various sophists try to sell.
What they try to sell is how one spends those limited hours, and more specifically - who do we serve in that time. Those few do have the illusion that life is not a zero-sum game. Until death presents them with the winning argument.
That's not what zero sum means. It's not zero sum just because you eventually die. Every person has different goals and it's entirely possible for them to come out ahead with respect to their goals.
Carefully managed, this is not locally zero sum, and we can all benefit. Unfortunately, that doesn't satisfy some people, and they use their resources to disproportionately acquire even more resources until the peasants are left fighting for scrap.