Braden Cox at TLF blogs on Google's argument that censorship is a trade barrier. There's a news story here. And Andrew McLaughlin blogs here. I'm astounded that this line of argument hasn't already been presented (as of course it has with the US prohibition on Internet gambling).
But will it fly? Moral arguments may hold greater sway with the public. The EU is unlikely to let go of its cultural exceptions to free speech, be they greater restrictions on political speech than we tolerate here, or on medical information, or language preferences. The Chinese government is well aware that it will face problems both giving people the access to information that a modern economy needs, and keeping a handle on social unrest and dissent. Some pressure though, might be productive (I'm more optomistic on this point than Braden).
The down side: in DC culture, the classic response to other nation's trade barriers is to persist in maintaining those of our own. This not only deprives those who would go forward with trading within our own economy. It deprives citizens of the foreign nation who may not have any control whatsoever over their government's policies (or no control, in the case of China), and whose free speech rights we are supposedly upholding. How do you punish a foreign government without hurting its citizens? Not an area in which I have expertise, but there is surely a better way.