Yes early researchers were wildly optimistic. I don’t see how that makes them arrogant. Other disciplines had followed much quicker paths to success. Say the Wright Brothers to the first Jet Plane or the Manhattan Project and the bomb. However it didn’t have to be that way. The Wright Brother’s early success could have been followed by decades of stumbling along only to make small progress because of unforeseeable reasons. I guess you would have mocked those early aviators as poor arrogant fools as well.
It is often the nature of problems not to know the magnitude of the obstacles until you commit resources to solving said problem.
Similarly just because a problem has persisted for a long time, doesn’t mean it can’t be cracked. Superconductor research is an example of something that languished a long time, then suddenly flourished. I suspect both Nuclear Fusion and Strong AI to be cracked within the next 2 to 5 decades.
Early strong success are usually an indicator you are on the right track, not the opposite.
Ray Kurzweil’s predictions may be over hyped, on the other hand may of his predictions have come true, many to a great degree of accuracy, others less so, or slightly delayed, but hardly wildly wrong.
Show me your great accomplishments that show why these people shouldn't "persist in their stupidity"