Even if the person doing the killing makes no effort to explain why? And, quite honestly, that makes you sound a psychopath. Normal people tend to react far less understanding in such a situation.
Actually, your argumentation makes more sense when there aren't any stakes, as would be the case here. No matter what happens, we won't be affected by it so we can afford to risk letting somebody destroy the world to see if it was worth it.It's not that east to relate to because we don't really HAVE stakes like that in the real world. But we can have them in fictional settings.