This appears to have big stakes for free speech in general, not just climate science. We need people to be allowed to disagree - yes, even in the face of data.
Virtually every country on Earth has laws that apply when you make false accusations that cause real-world harm, and there is a long history of such trials in the US, so I fail to see how this has "big stakes for free speech".
You are making an assumption as big as the Ozone Hole. Er, I mean as big as it used to be. /s
Hmm, so no legal responsibilities for companies spreading harmful propaganda?
Yes, it needs to be legal to be wrong, and it needs to be legal to lie when not under oath.
I don't want advertisers and shopkeepers lying to me about their products. I don't care if they're not under oath. I'd rather they not be allowed to scam me into buying their worthless goods.
Beyond that, if "free speech" trumps proof of harm or criminal intent, then all forms of fraud would be legal. Fortunately, the legal system is not that stupid.