Can someone elucidate why existing defamation laws don't cover this already?
Case in point: the dairy abuse video that was shot (let agree, it was bad). I've seen it rework and targeted at a milk creamery in Oregon (all via YouTube and Facebook). The video state that this was how the Oregon creamery treated its cows. Couple problems: the dairy wasn't in Oregon, it was in Idaho. The dairy in Idaho doesn't sell to the creamery in Oregon. And the creamery in Oregon DOESN'T OWN ANY COWS. They contract their milk from dairymen in Oregon.
If the film is popular (and therefore does more damage), the filmmaker will probably have the means to adequately compensate the farmer. If it isn't popular, it probably won't do much damage to the farmer.
Limiting free speech isn't a good solution.