Criticizing the Critics

OK, what, really, is the function of criticism, or, specifically, of most of the literary criticizing that goes on, from Poetry magazine to attack-mode blogs? To teach and enlighten the reader? To impose one's own aesthetic? To suppress what you personally dislike or consider inferior (to suppress through intimidation)? To protect your own turf? It seems like that's what it's all about. I love someone's take on a poem or a poet that gives a new angle, a thought I never had before, something that enlarges the work. I hate reading criticism driven by some form of envy or threat, or worse, that's meant mostly to make the reader think the critic is pretty damn smart. Hubris seems to be high on the list here of what characterizes literary critics.