Moral relativists; Do you believe in concepts like "fairness" and "justice" if so why?

You're right, but in striving to retain them you're grasping at straws. There are no moral absolutes just what is good or bad for your side. Even from an objective point of view justice has never been defined. Plato spent hundreds of pages trying to do so in his Republic over 2000 years ago, failed, and we've come no closer to a definition since.