Richard Haass wants a “robust” response to the use of chemical weapons in Syria:

It is essential to respond directly and meaningfully to any use of such weapons so they are not used again by the regime. But the reasons for a strong response transcend Syria. It will be a very different 21st century if weapons of mass destruction – whether they are chemical, biological or nuclear – come to be seen as just another type of weapon. There needs to be a robust taboo surrounding their use. Any leader must know that a decision to deploy them will sacrifice sovereign immunity and result in many in the world accepting nothing less than ousting and arrest.

Since almost all countries are parties to the Chemical Weapons Convention, there are very few governments that are likely to treat chemical weapons as “just another type of weapon.” In spite of the Syrian government’s use of these weapons, the taboo against their use is already very strong and not likely to be violated by any of the states that have agreed to the convention. The norm that Haass proposes is one that probably won’t be consistently enforced in the future, and it cannot be effectively enforced in the Syrian case without making a larger military commitment than he is willing to support. It is all very well to insist on such a norm in the abstract, but in practice punishing the Syrian regime for its chemical weapons use would require a lot more than the few airstrikes that Haass recommends.

Once the U.S. starts attacking regime targets inside Syria, it will have openly joined the war in Syria. If the “limited action” Haass wants fails to stop additional uses of chemical weapons, the U.S. will be pressured to continue escalating its involvement until the Syrian government is overthrown. After the regime is defeated, Syria’s chemical weapons arsenal will no longer be secure, and these weapons will go to whichever group can seize or buy them first, and it is even less likely that these groups will respect the taboo against their use.