I have also seen instances where nearly an entire field is making some elementary error, which people outside that field can see more clearly, but which they can't communicate to people in that field because they would have to spend years learning enough about the field to write a paper, probably with half a year's worth of experimental work, and not get rejected, even if their insight is something that could be communicated in a single sentence.
I think that you're saying that the outsiders can't be published without learning the jargon and doing experiments. But publication is not the only avenue. If it really only takes a single sentence, the outsider should be able to find an insider who will look past jargon and data and listen to the sentence. Then the insider can tell other insiders, or tack it onto a publication, or do the new experiments.
If jargon is not just a barrier to publication, but also to communication it's a lot harder to find a sympathetic insider, but it hardly seems impossible. Also, in that situation, how can outsiders be sure they understand?
These situations sound like there is a much bigger problem than the elementary error, perhaps that the people involved just don't care about seeking truth, only about having a routine.
"These situations sound like there is a much bigger problem than the elementary error, perhaps that the people involved just don't care about seeking truth, only about having a routine."
Well, a large part of it is funding/bureaucracy/grants. I tend to thing that's the main part in many of these fields. Look at Taubes's Good Calories, Bad Calories for a largely correct history of how the field of nutrition went wrong and is still going at it pretty badly. You do have a growing number of insiders doing research not on the "wrong" path ...
David Stove's "What Is Wrong With Our Thoughts" is a critique of philosophy that I can only call epic.
The astute reader will of course find themselves objecting to Stove's notion that we should be catologuing every possible way to do philosophy wrong. It's not like there's some originally pure mode of thought, being tainted by only a small library of poisons. It's just that there are exponentially more possible crazy thoughts than sane thoughts, c.f. entropy.
But Stove's list of 39 different classic crazinesses applied to the number three is absolute pure epic gold. (Scroll down about halfway through if you want to jump there directly.)
I especially like #8: "There is an integer between two and four, but it is not three, and its true name and nature are not to be revealed."