As humans we are dangerously incapable of reasoning about most of our increasingly complex worlds' and societies' mechanics, while forming opinions about them easily and quickly. We treat hard to reason about issues, that are not a matter of opinion, as if they were.

In this contact bias plays a huge role: The more people are subject to a topic, the more important it will be to them. And the more people are subjected to the idea of x being true on that topic, the more people will think of x as true.

I can easily believe that YouTube (as in "the code") does not have an unfair and systemic bias towards climate denialism. But yeah, if the algorithm pegs climate denialism videos as content that keep people engaged (maybe because it keeps them enraged) and keeps feeding them to more people, then I have no doubt that it statistically will convince more people of those ideas – and that is an issue.