[scaramanga]

Furthermore, the "this person is a jerk" part is clearly not part of some dispassionate evaluation of his professional accomplishments and is just a verbal attack couched in the language of professional criticism.

I suspect that, in many instances, people who do that are not trying to convince anybody of anything. If they expected to be greeted everywhere with agreement then they would not go around saying things which they know perfectly well are not likely to result in a vigorous and healthy debate if they were said to strangers in the street :)