I feel ya, I also generally am very against "it's just common sense!" type reasoning. But have you ever spent time with, like special education students? Like someone who will need to live with their parents forever because they can't learn to do things like read or write? It's nice to believe that maybe if only they had been given the right environment, they wouldn't have those problems - it's also just not true. Or perhaps we can take a more extremely example of someone who suffered a major brain injury. It sucks, and it's unfair, but at the end of the day some people really are definitively less smart than others. And by that same token, those others are definitively more smart than them. Of course, once people are at a certain level, it gets a lot harder to tell, but that dynamic is still in play. Likewise, if you've ever had the experience of interacting with a gifted kid, it's pretty clear that they're smarter than others.

That's a good distinction about intelligence being generally advantageous. That is why I said generally - it has some clear disadvantages like loneliness or a deeper awareness of the world's problems, etc. But most of the time, being smart is advantageous, don't you think? I mean, what is intelligence other than an ability to correctly understand reality? I do agree that sometimes having a false understanding of reality can coincidentally help you out, but knowing how things really are is certainly the superior strategy. If you think otherwise, it's always easy to make yourself dumber and reap the rewards. I don't mean that sarcastically or cruelly. I just mean, there's a reason we don't see intelligent people lobotomizing themselves to have better lives.

Agreed the chart only shows correlation and not causation in either direction.