Goal-directed agents who are forced to signal their opinions to others can benefit from voluntarily deceiving themselves in order to effectively deceive others. Their self-deception makes their opinions more credible - since they honestly believe them.

This seems to reflect human cognitive architecture more than a general fact about optimal agents or even most/all goal-directed agents. That humans are not optimal is nothing new around here, nor that the agreement theorems have little relevance to real human arguments. (I can't be the only one to read the papers and think, 'hell, I don't trust myself as far as even the weakened models, much less Creationists and whatnot', and have little use for them.)