False flags in Syria
The Obama Administration cooperating with rebels to frame Assad for using WMD? Why, next you're going to tell me Obama's Justice Department would fling thousands of guns across the Mexican border into the waiting arms of drug cartels, without making a serious effort to track them.
Seriously, I'm a little skeptical of false-flag theories, but I'm also a little skeptical of the "slam-dunk" case for Assad gassing his people. It's really tough to get slam-dunk evidence out of a war zone. A lot of the intel community's confidence comes from intercepted Syrian army chatter. There was a good deal of low-level Iraqi military chatter about Saddam's nukes, too. I've heard it theorized that Saddam really thought he had some nuclear warheads, because terrified underlings assured him they were in stock.
I'll assume the various intelligence services, both American and foreign, have executed due diligence on these Syrian army communications, and confidence in their authenticity is reasonably well-founded. That still doesn't get us to 100 percent certainty, or even 90 percent. I think I'm about 70% confident the Assad regime executed the gas attack, and perhaps a bit less than 50% confident Assad himself ordered it.
It's the contemplation of motive that drives much of the uncertainty. The Assad regime had little to gain by deploying WMD - they're winning the civil war anyway, and they've killed much larger groups of people using conventional weapons. It seems almost unbelievably stupid of them to spray sarin gas around when UN weapons inspectors were in the country. The rebels, on the other hand, have a great deal to gain from convincing the world community that Assad crossed that fabled "red line."
I'd still have problems with the way Operation Just Muscular Enough To Avoid Being Mocked was shaping up, even if I was completely convinced Assad had deployed chemical weapons. But the degree of uncertainty about his culpability is large enough to be significant. Conversely, he's already murdered enough civilians to be a war criminal many times over, whether he used poison gas or not. And he's not the only dictator currently in power to meet that criterion.