While I always thought the nick-name was supposed to be all the things already mention, positive and negative.
Nothing is as it appears or can be neatly catagorized.
One of the points of the show was that here were basicly good people doing nasty things for usually good reasons. So, they were there to stem the flow of chaos, but if it required hitting someone from behind with a sandbag, so be it. Anything to get the job done.