Throwing your hands in the air and saying "well we can never know for sure" is not as accurate as giving probabilities of various results. We can never know for sure which answer is right, but we can assign our probabilities so that, on average, we are always as confident as we should be. Of course, humans are ill-suited to this task, having a variety of suboptimal heuristics and downright biases, but they're all we have. And we can, in fact, assign the correct probabilities / choose the correct choice when we have the problem reduced to a mathematical model and apply the math without making mistakes.

If all you're looking for is confidence, why must you assign probabilities? I'm pushing you in hopes of understanding, not necessarily disagreeing. If I'm very religious and use that as my life-guide, I could be extremely confident in a given answer. In other words, the value of using probabilities must extend beyond confidence in my own answer -- confidence is just a personal feeling. Being "right" in a normative sense is also relevant, but as you point out, we often don't actually know what answer is correct. If your point instead is that probabilities will result in the right answer more often then not, fine, then accurately identifying the proper inputs and valuing them correctly is of utmost importance -- this is simply not practical in many situations precisely because the world is so complex. I guess it boils down to this -- what is the value of being "right" if what is "right" cannot be determined? I think there are decisions where what is right can be determined -- and rationality and the bayesian model works quite well. I think far more decisions (social relationships, politics, economics -- particularly decisions that do not directly affect the decision maker) are too subjective to know what is "right" or accurately model inputs. In those cases, I think rationality falls short, and the attempt to assign probabilities can give false confidence that the derived answer has a greater value than simply providing confidence that it is the best one.

I think I'm the only one on LessWrong that finds EY's writing maddening -- mostly the style -- I keep screaming to myself, "get to the point!" -- as noted, perhaps its just me. His examples from the cited article miss the point of perspectivism I think. Perspectivism (or at least how I am using it) simply means that truth can be relative, not that it is relative in all cases. Rationality does not seem to account for the possibility that it could be relative in any case.