nods If it's someone whose name I recognize and whose opinion I value, that tends to get handled similar to an "expert's intuitive evaluation". I don't know how tight-knit the community is here, and what percentage of "I disagree" messages end up triggering that here, but most communities I've seen aren't tight-knit enough for it to be meaningful except possibly when said by a "tribal leader".

You do make a good point about the acceptability of "I disagree" influencing the acceptability of "I disagree because of this brief reason" :)