On top of all this, climate denialism is such a fuzzy topic. The science community barely even agrees on many aspects of the data and potential remediations. My point is, whenever these content hosts start adjusting recommendations based on their view of the world, regardless of whether I agree or not, I think we’re all done a disservice. What YouTube’s management define as “reasonable consensus” is most certainly not going to be a moderate position.
I would argue it is very beneficial to promote flat-earther videos. Because most people can see it being false, and can use the experience to learn to not trust to everything. So it can be a kind of a vaccine.
Some people who watch those videos will be convinced the earth is flat. But even the people that don't, that "use the experience to learn to not trust everything", is also harmful. It's far more productive for YouTube, or any institution, to build actually trustworthy institutions, rather than teaching people to not trust anything.
This isn't a free speech issue, no one is suggesting that this content be removed from the internet.
The issue is that sites like YouTube don't just provide content, they also promote it by showing people recommendations. No one is suggesting that climate change deniers should be prohibited from expressing their views, just that YouTube should not promote it.
Take a more extreme issue: flat-earthers. Someone who believes the earth is flat should definitely be able to say so, but it's not a good idea for YouTube to actively promote that viewpoint. It's also just as bad for YouTube to present the issue purely as flat-earthers versus non-flat-earthers, as it suggests there is some sort of balance between the viewpoints.
To the extent that YouTube is promoting content, they should do within some bounds of reasonable consensus. If they refuse to police their recommendations, they aren't improving free speech, they are just destroying the existing mechanisms of consensus.