In the Elder Scrolls games (Morrowind and Oblivion, to be more specific), neutral/good characters will attack you if you hit them. Of course, if you killed certain 'good' characters, the game would tell you that the story can't continue on, but you can still keep playing. I remember meeting the God, Lord Vivic, in the Morrowind game and pummeling him to his death with nothing more than my bare hands just because I thought that it would be funny.