Maybe, or maybe you just insufficiently observed the variability across cultures or time, or ignored it, or pretended the outliers don't contradict your cherished thesis, or pretended your sample set is more representative than it is, etc., etc. Anyway "pretty good" evidence seems about the right standard for something to be labeled a just-so story.
Consensus is the best you can ask for with evolutionary stories. There is no equivalent of a mathematical proof in that field. Do you think we shouldn't bother with this field of study at all since we cannot definitively prove something?
In a world where the worst sort of racist dogmas proceed from exactly this sort of reasoning, and where natural selection is often made to stand in the place of God ("the fittest survive"), maybe we should.
Well, I was going to make a comment that this sort of "just so story" logic is prevalent amongst those who are anti-evolution (e.g. creationists) and would rather see the idea die, but it seems I do not need to.
Haha.. Nope, I'm not a creationist. I do have a Phd mostly earned studying evolutionary biology, though (sequence conservation). Thats why I detest this form of logic so, I understand better than most how limited our insight into adaptive cause is. When I started grad school I imagined I would be able to explain all of what made humans special by examining human-chimp divergence. It didn't take too long to disabuse me of that notion.