but you don't go far enough IMO. In a situation of international anarchy norms - not laws - will be enforced by those who can and have the will. If they are not enforced, the norms lose their status as norms (incidentally one of the few times I agree with my President even though I don't believe he has any intent or will to enofrce the norms he verbally champions). If the norm not to use chemical weapons is upheld by the US - not very likely at the moment - then it will be a long time before a state or leader is tempted to risk the consequenses by using them again and by extension other WMD. If, on the other hand, there is little or no cost to Assad for using chmical weapons he will likely use them again and others will be tempted to push against the limits of other treaties like the NPT and, perhaps use other unacceptable weapons.

Let me return to the prior point: All international law is ultimately consensual and enforceable only by the strong in coalition or alone. the highest legitimacy in enforceing IL against a transgressor is gained if the UNSC is able to act - that is the Great Powers agree and are joined by enogh lesser powers on the UNSC. Then, and only then, is the "law" enforced. Otherwise, a norm is enforced by one or a coalition of powers.

Cheers

JohnT