Curiously, participants in discussions of all of these subjects seem equally confident, regardless of the field's distance from experimental acquisition of reliable knowledge. What correlates with distance from objective knowledge is not uncertainty, but controversy.
Are you sure "distance from objective knowledge" is the best x-axis to make this observation? "The closer you get to humans, the worse the science gets" is a fairly common quote, supposedly (?) from W. Elsasser. That fields more directly involved with humans are less rational is not surprising : practitioners of such fields see the direct relevance to people's lives as a good thing and gain status from it. Attempts to make these fields more rational (carefully-defined terminology, good statistics, computerised data-gathering and analysis,...) will appear to move such fields away from "directly relevant to people's lives" and towards "irrelevant academic ivory-tower practices".
The earliest I've managed to trace the phrase "The closer you get to humans, the worse the science gets" is a blog comment by David Marjanović July 13 2007. He claimed it was a proverb. Someone else in the thread then claimed "that's pretty much like a folk heuristic version of Walter M. Elsasser's 'Reflections on a Theory of Organisms: Holism in Biology'". I've been asking around for a better source, but it certainly doesn't seem to be something Elsasser said in those words. Marjanović is fond of it.
Edit: Found an earlier rendition, &q...
Half-closing my eyes and looking at the recent topic of morality from a distance, I am struck by the following trend.
In mathematics, there are no substantial controversies. (I am speaking of the present era in mathematics, since around the early 20th century. There were some before then, before it had been clearly worked out what was a proof and what was not.) There are few in physics, chemistry, molecular biology, astronomy. There are some but they are not the bulk of any of these subjects. Look at biology more generally, history, psychology, sociology, and controversy is a larger and larger part of the practice, in proportion to the distance of the subject from the possibility of reasonably conclusive experiments. Finally, politics and morality consist of nothing but controversy and always have done.
Curiously, participants in discussions of all of these subjects seem equally confident, regardless of the field's distance from experimental acquisition of reliable knowledge. What correlates with distance from objective knowledge is not uncertainty, but controversy. Across these fields (not necessarily within them), opinions are firmly held, independently of how well they can be supported. They are firmly defended and attacked in inverse proportion to that support. The less information there is about actual facts, the more scope there is for continuing the fight instead of changing one's mind. (So much for the Aumann agreement of Bayesian rationalists.)
Perhaps mathematicians and hard scientists are not more rational than others, but work in fields where it is easier to be rational. When they turn into crackpots outside their discipline, they were actually that irrational already, but have wandered into an area without safety rails.