Just how stupid were the ancient Israelites?

[Mystic]

If there was anything rational about their decision it would not be so condemned.

However, keep in mind, the golden calf started moving due to a sorcerer's magic, and they equated that power with the power displayed by Moses.

And Pharaoh's people disbelieved because they equated Moses' miracles as well with their sorcerers, and so the question arises, how to distinguish between a true miracle and not one.

And this is why the talk of Jacob and his name "Israel" is important, because, yes, might of power to a degree does verify you being right. But only at a very very high level.