Mike, agreed. And even when the evidence is staring them in the face, they will deny it to everyone else…
About 15-20% of any particular population suffers from this affliction. It mainly relates to a deep-seated fear of standing in contrast to what they believe is the overall consensus of the people around them. They fear being singled out and 'cast out of the tribe" so to speak. It is an elementary survival instinct that is dictating their 'denialist’ tendencies. They honestly believe what they are saying. When the majority start understanding the existence of atmospheric chemical spraying, for example, these very same denialists will flip, and start defending this fact, simply to keep fitting into majority consensus – and then they will honestly believe the counterpoint to their original point. It is simply a knee-jerk preservation tactic and most of them do not even realize that they are doing it. There are plenty of research articles about this psychological/sociological group-think behavior on the internet. One of the most recognized studies in this area is called Solomon Asch’s Line Experiment. Go look at videos showing it in action – it is quite enlightening.