As I don't believe there is such a thing as objective morality (including any sense of objective justice), I cannot see how coming up with a "universal code" could possibly make sense. Any code established would be, at best, acceptable to some and objectionable to others. The code would almost certainly be an arbitrary assertion of one group's preferred norms, and if it were mutually negotiated across many regions, it's content would be near zero. (Is it okay to abort a fetus? Some people see that as heinously unjust. Is it okay to punish a rape victim for "shaming" the family? Some people would object to a code that says it is not. Should we use capital punishment, or not? More than half of the nations on the Earth still have laws permitting it, and there is no reason to suggest that only wealthy or industrialized nations, where it tends to be banned, get a say in what goes in the code. Etc.)
Better to let local people develop their own rules of fairness and justice and apply them in a way that the community as a whole tends to agree with. In an ideal world, with relatively free flows of people from nation to nation, we could them choose to live in the place that comes slowest to our image of the ideal, even if that image would be entirely rejected by people in another tradition.
On a naive level, part of me likes to imagine the world would be better off of everyone lived by my moral and ethical norms, and I struggle not to apply them to people in situations dissimilar from my own. That said, I have realized that my naive and emotional self is wrong and that letting people be free to pursue their own beliefs will lead to a better world than the one in which I am the arbiter of right and wrong.
