What's the point of bombing Syria?

I'm getting increasingly concerned at the US, UK and French war drums being beaten in anticipation of bombing Syria to punish them for nerve-gassing civilians. Don't get me wrong, I think that the use of chemical weapons at all is deserving of severe punishment, and if we can identify the military unit responsible for killing hundreds if not thousands of civilians with nerve agents then it should be bombed so hard that "they'll have to pipe in the sunlight"; a good few 2000lb LGBs to break open their shelters, napalm or white phos to burn up the munitions, and a healthy sprinkling of cluster weapons to finish off anyone left standing. At the very least, it will cause other chemical weapons unit commanders to think very hard about whether using their munitions really is in their personal best interest.

However it seems that the Syrian government didn't know this attack was coming, and indeed were rather horrified when it did according to US communications intercepts:

...in the hours after a horrific chemical attack east of Damascus, an official at the Syrian Ministry of Defense exchanged panicked phone calls with leader of a chemical weapons unit, demanding answers for a nerve agent strike that killed more than 1,000 people," the report said.

Now I don't know how much credence to give to this report, but it certainly fits well with observed behaviour; the US and UK now seem very confident that the Syrian government forces were responsible, yet there's no obvious gain - and much potential loss - for the Syrian government itself. Assad and company haven't survived this long by being pointlessly brutal. Even arch-tyrant Saddam Hussein of Iraq had method to his brutality: it was focused on keeping him in power, with him personally shooting senior ministers and officers if he even suspected a threat to him. Bashar al-Assad similarly is a survivor and not one to give Western forces a casus belli to open direct hostilities against him.

Bombing random airfields does nothing to deter the regime from using chemical weapons; quite the opposite. It certainly hurts their war effort, but it wasn't really triggered by government decisions in the first place. The Syrian government can certainly try to get more strict control of their weapons, but this action is punishing the government (however revolting) for actions outside their control. I'm not sure it really sends the right message. I'm also not convinced that the current opposition forces are necessarily the kind of people we want to back.

Update:
Matthew Inman at The Oatmeal pretty much nails my discomfort.