By sharing the accountability, you are reducing Little's. The bartender isn't responsible for those people's deaths; neither is society, or Leonard's mother, or Tupac, or Nintendo. The guy who got drunk and wrecked his car into somebody else's is. By taking full responsibility from him, you are alleviating the full consequences from the guy who actually committed the act, and that is wrong.
If you want to stiffen penalties for people who get drunk and run over somebody, you'll get no argument from me. But don't try to blame somebody else--even in part--for the criminal actions taken by an adult.