simpleton
Different from the older usage, the newer usage of the term refers to people to over-simplify every concept.

Just like there is Asperger's that is a functional version of autism, a simpleton is a functional version of the idea of an "idiot-savant." A person who can be very smart but also over-simplifies everything.

A black-and-white thinker.
"Wow, that guy is a really great programmer, but he's such a simpleton when it comes to politics and economics"