The above musings do not hinge on the ratio of people in a group believing things for the right reasons, only that some portion of them are.

Your consideration helps us assign probabilities for complex beliefs, but it doesn't help us improve them. Upon discovering that your beliefs correlate with those of your parents, you can introduce uncertainty in your current assignments, but you go about improving them by thinking about good arguments. And only good arguments.

The thrust of the original comment here is that discovering which arguments are good is not straightforward. You can only go so deep into the threads of argumentation until you start scraping on your own bias and incapacities. Your logic is not magic, and neither are intuitions nor other's beliefs. But all of them are heuristics that you can account when assigning probabilities. The very fact that others exist who are capable of digging as deep into the logic and being as skeptical of their intuitions, and who believe differently than you, is evidence that their opinion is correct. It matters little if every person of that opinion is as such, only that the best do. Because those are the only people you're paying attention to.