Why is Syria Using Chemical Weapons?

According to the latest reports, like this one in the NYT, al-Assad’s regime conducted an attack yesterday in Syria using a nerve-agent against the rebel forces there. Now these reports could be untrue for al-Assad and his staunch ally
Russia, claim that these are false reports transmitted by the rebels in an effort to provoke the U.S. and other Western powers to aid them in their fight against the loyalists and Hezbollah. But according to what I’ve seen today, unlike other times the rebellion has claimed to have video of victims of nerve gas, these look very convincing.

Now, if the al-Assad loyalists and Hezbollah are really using WMD’s against the rebels now, I have one question: Why?

The ruling regime is winning the war. They have Russia backing them almost 100%. Why would they risk the advantageous position they currently hold when using chemical weapons may provoke the U.S. and the U.N. into taking action against them? Why would they cross Pres. Obama’s metaphorical “red line” that he has drawn regarding the use of chemical weapons?

I know that crazy things happen in war. And maybe the use of a chemical weapon was not ordered from high-above but by a low-level officer and that is why al-Assad and Russia are denying ithese reports so vehemently. Maybe some even lower-level troops put together what was reported by the NYT, a make-shift missile which was launched in this attack because they just got tired of seeing their buddies killed and opted for revenge instead of a more rational approach to war.

But maybe the regime is that irrational for killing your own citizens is always an irrational act.