I like this post, and here is some evidence supporting your fear that some people may over-use the morality=logic metaphor, i.e., copy too many anticipations about how logical reasoning works over to their anticipations about how moral reasoning works... The comment is already downvoted to -2, suggesting the community realizes this (please don't downvote it further so as to over-punish the author), but the fact that someone made it is evidence that your point here is valuable one.

http://lesswrong.com/lw/g0e/narrativeselfimageand_selfcommunication/83ag