In other words, even when they had ample evidence with which to differentiate, they went with their biologically programmed attraction to confidence rather than their rational assessment of expertise. I'm vulnerable to it too; I just added an extremist Libertarian as a friend on Facebook, because they're just so enjoyable to talk to.

Occam's razor suggests that it's more likely, given this one data point, that it's true of all people than that it's only true of the people that happened to be in the sample. But that clearly doesn't justify holding that view very strongly; it's based on a small amount of evidence.

If human beings can't recognize nuanced, tentative conclusions as a sign of expertise, they definitely have a problem.

Well, I can recognize this statement as an unsubstituted, cocky declaration rather than a nuanced, tentative conclusion.

Arrogance hinders people from getting smarter.