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.