This sort of misses the idea of competency not being cross compatible to different areas, or over confidence causing blind spots where you may otherwise be highly competent. Some times the best marks for scams aren't the stupid, but the ones smart enough to delude themselves into thinking they know how to take advantage of a situation, and often dig themselves further in thinking they can work their way out.
Ultimately what we all need to work on, smart or stupid, is authentically listening to feedback and self-reflection.
Yes, that is exactly the reason why i believe the core issue is not stupidity and IQ itself, but rather that miscalibration between The Real you and The Perception of you. If we cynically thought we had a stupidity problem on our hands, we actually have a much more serious and pervasive one: the self awareness one.
Actually, I guess I'm kinda cynical and think that it IS a stupidity problem. As information is acquired, it takes a lot of intelligence to properly contextualize it and turn it into knowledge. Information that concurs with our established knowledge base is relatively easy to process. Information that challenges it is much more difficult as it requires reevaluation and re-contextualization of the parts of your knowledge base are now invalid. The deeper into that knowledge base the challenge, the harder the task.
Your brain discards millions of bits of information from your senses every second due the limits of what it can actually process. It doesn't seem like a reach to me to surmise that you also filter knowledge you can't process either. How else can you explain the lack of insight and critical thinking on display by the "fake news" crowd?
In a way this highlights another reason to not become over-confident in your self perception. It's a lot easier to process critical feedback when you don't already assume you're amazing.