I have mostly avoided comment on Syria, one of those things in my wheelhouse, professionally, but as always, Mungowitz knows how to get me to break my silence. Distaste for A Man for All Seasons aside, the "cut down the law to get the devil" argument doesn't really work here.
Why? International criminal law has always had an element of that: states and leaders who are likely to violate particular potential laws try to avoid or shun legal obligations, everyone recognizes this, and so a certain amount of 'cutting down to size' is part of upholding the moral principles that are not usually in conflict with the rule of law in domestic legal systems (this is also part of Arendt's point in Eichmann in Jerusalem: the reason why we can default to the rule of law is because the laws are usually good, and comprehensive. When they are either not good or not comprehensive, there are problems). Thus Nuremberg, which is as clear an example of setting aside all the basic rule of law principles as you'd like, and which most ICL textbooks are quite forthright about.*
The truth of the matter is there are three unappealing options, none of which is going to satisfy all the things we'd want from a legal system:
1. We can accept the rule of law and its outcome here, which would be no action at all, but also pretty much never any action no matter what the problem is, because that's what the UN regime is designed to produce as an outcome.
2. Act extrajudicially--the viable alternative to Nuremberg, for example, was summary execution, which seems clearly worse on a rule of law level. The United States has the power to do whatever it wants, for any reason or no reason at all, and the recognition of this needs to be a feature of thinking through these problems.
3. Recognize that legal norms shift more quickly than laws and, in a common law-like way, leave some space for new norms to emerge, which can be law-like without themselves being laws. (I understand Kerry has been using some language to this effect.) We could get into jus cogens and customary international law, but these are standard legal arguments in international law.
Now, I'm opposed to doing anything in Syria, not because I think there's anything morally or legally wrong with doing so, but because I think the American public rarely has the stamina for working through the long aftermath of intervention. But it also seems to me that when law and morality are in conflict, #3 is the option most able to balance the two.
*Having read through and taught the deliberations of the panel that formed the Nuremberg IMT law, I am reasonably convinced that Germany did nothing, or close to nothing, that was illegal in the planning or performance of World War II, and probably had a reasonable belief they were engaging in standard practices, or at least practices within the limits of acceptable war-fighting--and that all parties involved in the IMT deliberations were aware of this. They certainly had no reason to suspect that the standard Superior Orders or Reason of State defenses would be disallowed, as the IMT decided, nor that wholly domestic acts engaged in prior to the beginning of the war could be subject to an international tribunal, that jurisdictional grab being more or less the purpose in bringing about the category of Crimes Against Humanity (ie a Crime Against Humanity, in the IMT, is a claim that could easily be adjudicated in a domestic court without requiring any changes to the rule of law). That being said, I'd be hard-pressed to argue the IMT was not close to the best possible outcome.