If someone averages only the guesses from this subset, they’re ignoring the conditional selection effect, that the dataset (the set of guesses) is biased by the

If someone averages only the guesses from this subset, they’re ignoring the conditional selection effect, that the dataset (the set of guesses) is biased by the very act of being willing to guess. So the "average of guesses" doesn't represent the true expert population, and ignores the conditional selection effect. There's also just the reality that most of these experts have a lot of skin in the game, and there's lots of pressure in this world to a true believer, so I'm not going to buy into it too much.