Not right, ius, but right, rectus, as in "right reason," "That action is right," and the opposite of wrong.
Often relativism arises when one begins to doubt one's standards for right action, or fails to understand why an action is deemed to be right, how "rightness" is tied to good. The meaning of rectus is straight. So an action is right (or good) if it achieves the good that we should be aiming at, and thus is "straight."
Alisdair MacIntyre, following Elizabeth Anscombe, offers a different explanation of how this separation came to be, by looking at the history of moral philosophy. While there may be some value in his approach, I do question whether the musings of a select few really had that much of an impact on the populace. (Still, his explanation of the purpose of deontologists (primarily Kant)
to find some sort of basis of right in how reason works or applies itself to human action does make sense.)
I tend to think that this separation in the general population can be explained rather by an incomplete moral development, and the loss of tradition and obedience to the proper teaching authority(-ies). When we are growing up, we are told that certain things are right and wrong, and we act in accordance with the rules that we have been given by others. But as we mature we seek the reasons behind these standards, and if we do not get the answers, then some may be tempted to reject them as being "irrational" and not binding.
Now some may be able to intuit that some actions are right and wrong because they lead to or away from some good, and they can do this without the need for moral science. But if they do not understand moral reasoning, they may be lead astray when confronted with consequentialism, failing to see how right reason is not the same as consequentialist reasoning.
If the virtue of obedience is emphasized, and tied to charity, then a society can continue to flourish, even if most people are not educated in moral science or moral theology. But once the teaching authority of the Church is rejected, the value of tradition separate from authority cannot prevent those who are more daring from supplanting traditional norms with their own desires.
More on this topic to come, perhaps...