I've noticed a different motive for many of the more kooky science-deniers. I think that kind of denialism is rooted in their own insecurities about their intelligence. In essence, if they can rig up some quick way to prove the experts wrong, then they are smarter than all the experts. Another way of putting it is this: Rather than put in the hard work of understanding a difficult or nuanced argument, they come up with an easy solution that shows, in their mind, how smart they are.