Critics get a bad rap. It's the accepted wisdom that 'if you can't do, then teach, and if you can't do or teach, then tell people who can what they're doing wrong,' which is unfair to teachers (who--in my not particularly humble opinion--get a worse and infinitely more undeserved rap) and critics, both.
I would argue that besides acting as a convenient whipping boy for artists who are seldom the best judges of their own work, critics provide the valuable service of drowning out a lot of the inane palaver in the cultural conversation. Do they miss some very worthy work? Yes, oodles of it. Do they misjudge great works? Yes, certainly. Do they have personal biases and blind spots? Yep. Do they fall prey to fads and fashions that will ultimately be looked on only with derision and regret? Yes, just like you and me--how do you feel about those pea green jeggings you bought in a fit of hubris and reckless disregard for your credit score last month?