Can someone try to make that argument more precise? It seems to me that the claim "Sorry. It can't be done" sounds plausible but fails in the most obvious limit case: a proof of a mathematical theorem doesn't become less correct if I found it by deliberately trying to prove the theorem. Since Bayesian reasoning approaches classical logic in the limit, the claim might be wrong for Bayesian reasoning too.
In the spirit of contrarianism, I'd like to argue against The Bottom Line.
As I understand the post, its idea is that a rationalist should never "start with a bottom line and then fill out the arguments".
It sounds neat, but I think it is not psychologically feasible. I find that whenever I actually argue, I always have the conclusion already written. Without it, it is impossible to have any direction, and an argument without any direction does not go anywhere.
What actually happens is:
It is at the point 3 that the biases really struck. Motivated Stopping makes me stop checking too early, and Motivated Continuation makes me look for better arguments when defective ones are found for the conclusion I seek, but not for alternatives, resulting in Straw Men.