There is a clear logical contrdiction in this way of thinking. What you are talking about here is the potmodernism theory, however, if there is no absolute truth, can postmodernism be itself true?Indeed, if there is no right and wrong, there is no need to argue for the discipline of ethics in the first place.
If we were to go with your theory just for a second, and say that morality is debatable in every sense. Notice than in any ethical argument, one part or the other is clearly applying to a higher standard, or an absolute truth. In other words, an objective morality.
Also, when you do argue about a certain topic concerning morality, there is never a clear winner in this case. Meaning that if country A argued that child abuse was an obscene and disgusting act while country B argued that child abuse is perfectly normal. Under your theory ofcourse, country A does not have the right or the authority to be able to condemn country B. If the people in country B think child abuse is moral, then it is, and there is nothing you can do to stop them.
To take this further, all of these suicide bombers killing themselves to destroy other people's lives would then not be considered immoral. These terrorists truly believe that they are bringing good to their country, that they are defending their people, and protecting their families. Thus, why is terrorism at all immoral? If, again, you believe morality is merely relative, the world has no right at all to even mildly suggest that terrorism is an immoral act.