ALl those with fire damages should think about suing the Sierra Club. For decades the forestry service wanted to trim low growth and have periodic controlled burns (usually in zero wind and medium damp conditions) to clean out the understory growth left by clear and other tree harvesting. The Sierra Club fought this trimming - they wanted a 'natural forest' - get wise, goofs, a natural system uses fire from lightning to do just what happened.
More smaller fires are needed to head off these monster fires.
Even if your description was fully accurate, there's no cause of action against someone for lobbying for bad government policy, so other than a particularly expensive publicity stunt, I'm not sure what the point of such a suit would be.
I agree,they probably are not suable, protected speech, but we need to educate people to allow the forest renewal cycle to occur quite often, or you get huge build ups of fuel, and a very long dry spell like this one allow small burns to combine and grow, especially in high winds as we have seen