It's easy to acknowledge global warming exists, all of the nations that signed the Kyoto Accord agree there. But when it comes time to make the sacrifices necessary to follow it everyone copped out. So it is a valid argument against the film. It's the reason why Bush can get away with listing some magic bullet cures to the problem to avoid actually doing anything that woukd hurt the oil industry.
The whole argument that his overstatements and misuse of facts are forgiveable because they raise awareness is the same one used to defend Fahrenheit 9/11.