Micah Zenko explains why waging illegal war to enforce an international norm makes no sense:
The combination of Obama’s choice of norm enforcement by military means without the active participation of many other countries and outside of widely agreed-upon violation procedures explains why, although most countries agree that prohibiting chemical weapons use is an international norm worth defending, they overwhelmingly disagree with how the United States wants to enforce it in Syria.
The administration’s very weak case suffers from many problems, but one that seriously undermines it is the fact that there is a broad international consensus against what the U.S. has proposed doing. If almost all nations have accepted the CWC and agree that chemical weapons should not be used, it is fairly damning that the U.S. can’t get more than a handful of states to endorse the specific actions that the U.S. has wanted to take in Syria. Indeed, because almost all nations have accepted the CWC, the idea that the taboo against chemical weapons use is at risk makes no sense, and presumably many of the states that adhere to the convention see that.
As much as it will annoy Syria hawks to hear it, this is similar to the position that American Iraq war advocates and the Bush administration were in a decade ago, which resulted in an unconvincing effort to tell the world that illegal U.S. military action was the only way to preserve the foundations of international order. It was wrong then, and it’s still wrong now. Since “norm-enforcement” is the core of the administration’s case for intervention, the entire case falls apart when we realize that very few other countries acknowledge or respect U.S. justifications for the attack. On the contrary, the U.S. will be perceived as ignoring or even undermining the international system, and its reputation around the world will suffer accordingly.