For example, a certain group systematically kills another group and considers it morally right. Since there are no moral absolutes, the group can justify the killings by saying its their morals and they should be respected
Well take Germans killing Jews or Nigerian Muslims to Nigerian Christians. The Germans used a clever argument in the Nuremberg trials. They said Germany had decided Jews could be killed and that the allies were wrong in condemning them and imposing their cultures and moral laws on them
It all has to do with post modernism where you live in your own world and anything you believe to be true is true. That means you can believe morals exist or you can choose not to believe it, but its your personal reality and doesn't extend to others.