One thing you're overlooking, oogiedoogie, is that the film strongly implies that the Joker is a reaction to Batman. That Batman's flamboyant, melodramatic symbolism creates an equally flmaboyant, evil one. We most definitely do not "need such heros" if they just wind up creating more problems than they solve.
And make no mistake, oogiedoogie, Batman doesn't win at the end of this movie. It's at best a draw.