This is an actual comment made in a debate on one of the above topics, but I've altered the details a bit to focus on the commonalities and make a point about the true nature of the problem here. Can you tell whether this statement was made by an evolution denier or a global warming denier:
"You encourage those that are convinced that XXXXX is a serious threat to 'get involved'. You shouldn't be too surprised that those of us that don't see XXXXX as settled science would do the same. Despite your claim that XXXXX is based on "huge bodies of scientific knowledge", the fact is that XXXXX proponents have little to point to as hard evidence. The rest of the "huge body" consists mainly of speculation. I find it interesting that you characterize evidence that does not support XXXXX as 'misinformation'. We live in an open society where you are free to write books and give talks based on your personal opinion and the facts as you see them. Others, that hold different opinions based on their review of the evidence, share that same right."
Scary huh? See, the problem with denialists isn't the specific topic they are denying. The problem is that they reject the scientific process, and deny the reality of the progress of human knowledge. They put their trust in a discredited source of fact-finding, namely their own perceptions, rather than the tried and true scientific method of falsifiable experimentation, peer review, and replication. They deny the layered aspect of knowledge, where learning occurs in steps, and think that idly musing over an idea while sitting at their favorite barstool they are capable of coming up with an objection to a major scientific theory that hasn't already been considered by hundreds of people who know far more about the subject than they every will. Thus, their inclination to see no reason to do any actual testing of their hypotheses.
They would have you believe that because Einstein's relativity supplanted Newton's laws of motion, or that Piltdown Man was a hoax, that nothing scientists say has any more value than the opinion of the man on the street, who is, not coincidentally, them. How anyone can stand in the middle of this magnificent technological society man has built from, in the final analysis, literally nothing, and claim that we don't know any more than anyone else in history did, is beyond me, but that is the sort of intellectual relativism that lies at the core of denialism.