I think it's a bit of an exaggeration to say that someone playing like Turner is would warrant consideration of being benched if it weren't for contract and past performance considerations. This is by far his worst year, and his contract makes that more painfully obvious. But he is probably an average major league shortstop even as he is now. And I believe that even though I thought even before we signed him that Turner is not a great defensive shortstop, only average.
And even if he were a candidate to be benched, there really isn't a better option. I wouldn't expect anything better from Sosa, Kingery, or Weston Wilson.