It should be more troubling is if it looks like they were grappling with the right issues.
With regards to the Moravec's paradox, if you can't see how your AI idea will replicate behaviour of a cat (provided you have a cat), your notion of 'general intelligence' is probably thoroughly confused. If your AI needs to do something very superhuman to survive as a cat in the wild, likewise so. The next step could be invention of a stone tied to a stick, from scratch. If you think of AI doing advanced superhuman technology, your standard of understanding is too low.
if you can't see how your AI idea will replicate behaviour of a cat (provided you have a cat), your notion of 'general intelligence' is probably thoroughly confused
If you didn't know Moravec's paradox, and ranked the difficulty of cognitive tasks by their perceived human difficulty, then you'd conclude that any AI that could play chess could trivially behave as a cat, once you gave it the required body.
That's wrong, but there wasn't evidence for it being wrong, back in 1955.
I've just been through the proposal for the Dartmouth AI conference of 1956, and it's a surprising read. All I really knew about it was its absurd optimism, as typified by the quote:
An attempt will be made to find how to make machines use language, form abstractions and concepts, solve kinds of problems now reserved for humans, and improve themselves. We think that a significant advance can be made in one or more of these problems if a carefully selected group of scientists work on it together for a summer.
But then I read the rest of the document, and was... impressed. Go ahead and read it, and give me your thoughts. Given what was known in 1955, they were grappling with the right issues, and seemed to be making progress in the right directions and have plans and models for how to progress further. Seeing the phenomenally smart people who were behind this (McCarthy, Minsky, Rochester, Shannon), and given the impressive progress that computers had been making in what seemed very hard areas of cognition (remember that this was before we discovered Moravec's paradox)... I have to say that had I read this back in 1955, I think the rational belief would have been "AI is probably imminent". Some overconfidence, no doubt, but no good reason to expect these prominent thinkers to be so spectacularly wrong on something they were experts in.