I have not heard of a scammer fooling people in this kind of situation, but I have heard of isolated groups of professionals working for years on what turned out to be a mistake. The best example was Fedyakin et al. working on polywater. You might say everyone fooled himself. It was a group hallucination, sort of like a cult.
There have been examples of this in technology, such as really bad or non-working products such as at Theranos. There is evidence that Elizabeth Holmes and her closest staff members were engaged in fraud. Or at least, they knew the product hardly worked in some ways, and did not work at all in other ways. However, my impression from the book is that most of the researchers directly engaged in experiments were sincere. It often happens that things don't work and years of effort are in vain. That isn't fraud. That's how the cookie crumbles. If you knew it was going to work, that would be "development" not "research."
I do not think it is fair to say that the Theranos gadget was a complete fraud that did not begin to work, like some perpetual motion machines or Rossi's 1 MW reactor in Florida.
That is definitly possible. But for group hallucination and being a cult you dont need a small isolated group. The educated people in the middle age in europe where organized in a large group called the "catholic church", and they all thought that the earth is the middle of the universe - for centuries. The german society thought that jews are "unworthy life" for 10 years. The american society thought that communism is the death to all free people and has to be purged from the face of the earth for 40 years.
And my favorite hallucination:
For electrons and protons Maxwells laws do not hold but instead the laws of physics change magically when going from macroscopic to microscopic scale.... And atoms here on earth have a probability unequal to zero to be on mars the next time we look at them....
To find truth is no easy task for us humans. Thats because it is hard/impossible to estimate the true uncertainty of the information we rely our worldview/opinions on. And we can have a worldview and opinions even if we have no information on certain important aspects. In these cases we just have some generic assumptions with even higher uncertainty (in social context we call these generic assumptions "prejudice"). It is inherent to humans to underestimate the uncertainty of information. Otherwise it would be impossible for us to draw any conclusion and act accordingly.
There are cases in which small groups are hallucinating.
There are cases in which small groups are right.
There are cases where large groups are right.
There are cases where large groups are hallucinating.
I hope that we humans learn to first gain wisdom (and after that knowledge) to find good ways to deal with all these uncertainties. And yeah, I had a glass of wine