It is not vigilantism, it is the common law, rooted in ancient English history, of the "shire reeve", who we now call the "sheriff".
Reeve means "called", from the Germanic verb "rufen". In other words, this person is someone who is called to the duty by the shire. The point that has been raised about vigilantism is that the people taking action have not been appointed by the community and therefore are not answerable to the community, nor are there actions controllable in any way by the community.
The original duty of the shire reeve, among other things, was that he was 1 man out of every 10 households, whose duty it was to check the locks and gates of each house and barn, before himself retiring for the night.
In other words, this person checked the property of his peers. He was one of the community which selected him.
Each of the smaller networks connected to the larger Internet, has someone whose job it is to be sure that the "locks and gates" are shut.
And those network security people generally don't hang out on NANOG. Instead they hang out in various security forums like MAAWG etc. --Michael Dillon