That River in Egypt
Denial seems to be less a river than an archipelago. Those who disbelieve in science exhibit various degrees and types of crackpottery, but a few generalizations seem justified: science denialists tend to be ignorant, usually about almost everything, but sometimes just about their own bête noire; they also tend to be dogmatic, and uninterested in evidence; they are highly ideological, more interested in defending their own world view than in facts.
Evolution doubters are good examples of all three. A recent Pew survey looks at American vies of evolution and finds that about a third of Americans disbelieve in evolution. This disbelief is strongly correlated with religious affiliation and anti-correlated with education level. The level of stupidity/ignorance is a bit mind boggling to me. 33 % of the sample agreed with the statement:
“humans and other living things have existed in their present form since the beginning of time.”
I would be tempted to wonder that such people can feed themselves, except I suppose that their entire intellectual resources are devoted to just that task.
Vaccination denialists are another populous island group in the great archipelago. I don't know of similarly detailed information about them, but I have the impression that they are more of the new-agey, hippie, stoner, vaguely lefty persuasion.
Climate science skeptics sometimes fit the selective stupidity variation of my first unifying principle. One amusing technical blunder endorsed by many among them is the notion that atmospheric thickness, in and of itself, independent of the greenhouse gas content, somehow explains a phenomenon like the extreme surface temperature of Venus. Several otherwise intelligent guys, among them physicists and research meteorologists have made the claim to me that the perfect gas law explains the temperature difference between the surface and the effective radiating temperature of a planet.