Jon Lee Anderson assesses the situation:

Whatever the regime’s real intentions with regards to its chemical weapons, the next chapter in Syria will be an ugly one, and before it is all over, many people are going to die—from bullets and bombs if not from sarin gas. Thanks to the boy-who-cried-wolf legacy of the Iraq invasion and the W.M.D.-that-weren’t, it is not surprising that the alleged Syrian chemical weapons threat has thus far failed to cause panic in international circles. This could prove to be an unfortunate historical lesson, for, as things stand, there is no guarantee that they won’t be deployed. And if they are used, Syria’s conflict will become a threshold conflict in more ways than one.

Dominic Tierney ponders Western opposition to chemical weapons:

Strip away the moralistic opposition to chemical weapons and you often find strategic self-interest lying underneath. Powerful countries like the United States cultivate a taboo against using WMD partly because they have a vast advantage in conventional arms. We want to draw stark lines around acceptable and unacceptable kinds of warfare because the terrain that we carve out is strategically favorable. Washington can defeat most enemy states in a few days–unless the adversary uses WMD to level the playing field. 

Waldman adds:

That may be part of the story, but it's more than just strategicwe want to define our means of warfare as ordinary and any other means as outside the bounds of humane behavior, less for practical advantage than to convince ourselves that our actions are moral and justified.

Michael Crowley's related thoughts:

Unless he runs out of conventional weapons, Assad would be foolish to incite America by tapping his chemical arsenal. He’s spent most of the past two years inflicting blood-curdling suffering on his people. There’s little reason to think we’ll try to interfere–so long as his sadism is the conventional kind, the kind we apparently can tolerate.