However, the question whether or not humans end up totally extinct is relevant when comparing nuclear war with other very horrible risks, some of which do threaten total extinction. To discuss, prioritize and act on very serious (though, hopefully, unlikely to materialize) risks, we need a scale of "horribleness" that doesn't just give every serious problem a 10 out of 10. We need to reasonably prioritize our actions among many potentially dystopian risks - if consider a single one of them an negative infinity, a literal "AVOID AT ALL COSTS", then those "all costs" include increased vulnerability to other risks, and that's not appropriate.