Asking "Who are the worst denialists?" is a good question, because it makes us define what we mean by worst, and further it makes us really think about why this should matter to us. Sure, the moon-landing hoaxers are kind of fun, but are they really as bad as the anti-vaxxers? The anti-climate-change people? Physics cranks? The 9/11 Truthers?
So? Who are the worst denialists, and why?
Inspired by an article and comment section discussion at io9.