To put it simply, Bear, I do not want to school anyone about anything. I do not sustain a fragile ego, as you seem to do, with that want. I want only civilized discussion and exchange of ideas and information.
You clearly have no knowledge of this question yet want to try to bluster your way through and bulldoze others. You don't even seem to grasp where erga omnes does fit into the concept of the Right to self determination of peoples. Or that it is only peripheral to that question since it sheds no light on the factors that confer that Right.
You even talk of wanting to 'argue' the origin of erga omnes. Why, I cannot imagine since the question is about self determination of peoples. You, presumably, want to talk of the case in International Law in which the concept was framed.
Have you no idea that the origins are shrouded in the mists of history since, among others, it is concerned with property Rights that have been argued since Man first learned to speak.
Your wish is entirely off topic and should be in some separate discussion about Human Rights. That is one that I will not participate in since, though I have been very much involved and active in that are for many years, I have no wish to listen to hordes of people shouting about some pet idea.