Sure. I'm a fan of folk music, and it definitely suffers at the more didactic end. (I have a pretty high tolerance for explicitly political music -- I'm a Phil Ochs fan -- but there does reach a point where it isn't music anymore, it's an editorial set to a tune.) Art does its work below the rational level -- that means that good art is pretty much amoral, and it'll always take some wrangling to corral art into serving a purpose.