The rational reason to believe that would be internal company documents indicating that the company believed global warming was caused by fossil fuels. That's what this case is about: did they know one thing and say another and/or are there documents showing that they intentionally falsified data.
There are lots of contradicting documents to go by. There is not one study that either concludively proves or disproves the issue of global warming, or that man made factors are even the major cause of global warming. A company or individual should be allowed to express an opinion based on evidence that supports its points. The justice system has no business regulating what people should think, and why it thinks that.
Suppressing points of view that don't jive with group-think or political dogma is simply censorship. It stifles debate and scientific progress.
It is also unconstitutional in the US as far as the 1st amendment to its Bill of Rights.
If we follow the logic, then any entity that promotes the creationist theory should be prosecuted. Following the logic: the overwhelming evidence supports evolution and astrophysics theory. Yet, some people and organizations that actually run public services, or services available to the public such as schooboards, promote these views. Should they, in turn, be prosecuted for promoting 'false' notions? Those who say yes are promoting a Stalinist regime in the quest for the 'real truth'. Once we're in this boat, where does it stop? We're now into the realm of 'reeducation camps'.
Democracy can evolve into tyranny. That's when the majority imposes its will on the minority, for all kinds of self-serving reasons. The US founders were wary of tyranny, and that's why they guaranteed free speech.