Pretty simple role playing. Have you considered something a bit more evolved?
Indeed, I do have 'nice' chars who only use the black star on bandits and necros, but not hunters or random wanderers or those stendarr freaks. My current assassin, however, has no such scruples. But, outside of contracts, he doesn't usually mess with townies at all- although Nazeem has been just begging to get on my greatest 'hits' list...