Simply discounting self-bias in valuing a life doesn't give you a correct value. The opposite of self-biased is not unbiased.

I'm not sure it's even meaningful to put a dollar value on your own life. And, yes, we'd want to correct for the biases of hating the person in question, as well, which might lead you to undervalue him.

Human skills can be a positive resource. What ever skill are generated during a war, it does not take a war to generate those skills. Those skills could be developed in the absence of war. That those skills are not developed in the absence of war is not an argument I find persuasive that war has provided the benefit of the development of those skills.

I'm not claiming that war is the optimal outcome, only that it could be positive-sum. There may be other choices with an even larger sum. However, maybe the only way to exploit country Y's resources is with war; suppose all diplomatic attempts seem doomed to failure. Then, if the resources are valuable enough, war might be the best option (though we should also take into account how easy it is to underestimate the cost of war).

I don't consider that responses that people make to mitigate adverse circumstances can ever completely negate the adverse consequence. I think the idea that people have that a “silver lining” can completely mitigate an adverse event is part of the zero-sum bias the OP was talking about.

No, the zero-sum bias consists of erroneously thinking that an adverse event is always mitigated by a silver lining. Adverse events are sometimes mitigated by a silver lining. For instance, if you would freely choose to get a papercut for $10, and someone gives you a papercut accidentally, couldn't they mitigate the adverse event by giving you $10?