I am not talking about judging his 'worth as a person'; rather his 'worth as a developer.' Maybe in his private life he's a wonderful person, who knows? Who cares? It is his professional activities that concern people.
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 :)