Assad is backed by Iran, Russian and China. Our current policy is to support the Syrian rebels. What if Assad leaves the country and his forces, in desperation, launch chemical weapons on a rebel town?
Iran, Russia, and China could not back a regime that comitted international war crimes.
With them out of the way we can move forward with our agenda in the middle east.
See Iraq, Saddam Hussein, chemical weapons, kurds.
If the Syrians use Chemical WMD on Turkey, it will be WWIII going hot and full bore. At that point, international war crimes will be mute. Thousands will be dieing from Chemical and Biological attacks in the region.
With them out of the way we can move forward with our agenda in the middle east.
And that current agenda appear to be getting Chemical and Biological WMD's into the hands of Islamic Sunni terrorist organizations. You do not realize something. Russia, China and Iran now HAVE to stop the US. Obama's stupidity, ineptitude and cronyism has given them no choice.