My apologies for the delayed response. You have done a wonderful job arguing general or traditional rules. Unfortunately, I specifically intended to argue that states may change those rules through practice whenever they wish (except with regard to jus cogens norms of course).

On your first point to me, that: “Where an international obligation does exist, whether under a treaty or a rule of customary international law, a State is barred from invoking its internal law including its constitution.” I agree that this is an accurate statement of the GENERAL rule. My earlier point was that I do not accept at face value that this general rule is the ONLY possible rule with regard to every customary norm, particularly IHRL norms focused solely on matters of internal governance.

It is not impossible for states, in practice, to allow derogation from otherwise universal customary (leave aside treaty for the moment) IHRL norms to account for important or foundational constitutional requirements. They may do so even without persistent objection by the state with a contrary constitutional provision, if they so choose. I do not say that such practice exists or is established, but it is possible and would require analysis with regard to specific norms. Tossing about the general rule without examining or at least recognizing this possibility does nothing to address the potential for this normative development.

It is not necessary, as you later argue, to say that in such cases the rule never develops or lacks the requisite opinio juris. State practice and opinio juris itself may simply require that the norm truly be contrary to a fundamental constitutional requirement, otherwise it applies. Thus, to use your example, not all Islamic states would necessarily be equal depending upon the specific IHRL norm at issue (and whether it is jus cogens), its consistency with a requirement of Islam (as the state understands it), and a fundamental LEGAL requirement for the implementation of, or prohibition of interference with, Islam in a state’s constitution.

With regard to your discussion of the CEDAW, I will leave aside a broader discussion of treaty effect and interpretation and the possible effects of subsequent practice for now, but whether a reservation is consistent with the object and purpose of the treaty is first a matter for the states themselves to decide. If the greater object and purpose of a treaty is universal membership to advance the overall goals of the treaty to the fullest extent possible, then reservations with regard to significant elements of the treaty to account for fundamental constitutional requirements — even if they undermine those goals to some or even to a great extent — might be possible. Again, I do not here wish to assert that this has happened, but this thought may help us to understand the acquiescence of states to such behavior, and the lack of objections to such reservations. Of course, the lack of objections could also be evidence that other states believed what you assert is you assert is necessarily the case, that the reservation would never be effective. I simply seek other possible normative explanations that might reflect what we observe in the actual practice and diplomatic discourse (or lack thereof) of states in these areas.

I have not relooked our earlier discussion but do not think I argued that the ICCPR and ECHR are not equivalent in terms of the binding nature of their obligations. They are different in that the means of ECHR enforcement results in a delegation of the determination of the full scope and content of its norms to the ECtHR. States party to the ECHR, having delegated that power, are in a weaker position to refine the norm’s content through practice. Further, the ECHR contains specific norms which may or may not reflect universal customary law, or the INTERPRETATION of which may or may not reflect universal customary law . Thus, the content of its norms, as interpreted, may be significantly less relevant to the rest of the world. States simply retain greater flexibility with regard to the content of ICCPR norms, in part because of the enforcement mechanisms to which ECHR members have consented.

I do not see the need to argue over the persuasive force of various international tribunal decisions. Some opinions certainly have more force than others. I think it is fair to state that all such decisions have some, even if negligible, persuasive force. Contrary to what you assert, though, I think it is well established that some decisions become persuasive or influential IN SPITE OF the soundness of their reasoning or methodology.