How much evidence do we in fact have that the rebels gassed their own people in a false-flag operation? I had heard it was a possibility, Putin seems to think it's all but certain, but I haven't studied the issue in depth.
I'm of the opinion that you shouldn't go to war when the only reasoning behind it is evidence that you're fitting to your model.
Why would Assad use chemical weapons when he knows that the US is looking for a reason to invade?
He isn't an idiot.
http://www.theguardian.com/world/graphic/2013/sep/03/syria-c...
It isn't very good, it seems to be a case of finding scraps that fit your narrative rather than building a case.
One thing that leads me to believe that it might have been the rebels: the civilians and soldiers killed in that rebel controlled area around Damascus were part of the more moderate Syrian opposition forces. It is actually one of the few areas controlled by moderate opposition. It is entirely possible that the Salafists or more extreme al Qaeda associated forces carried out the attack using captured supplies. They dislike the moderate opposition about as much as they dislike Assad, and prompting US action suits them the most.