When a stupid person thinks too long about something they come up with worse views than what is generally accepted. When smart people think things through they come to better conclusions than what is generally accepted. Stupid people take christianity that is generally accepted think about it too long sometimes and take away the gospels and keep the god concept and add racism and all their likes and dislikes to it. Smart people are smart enough to know what is fair if they think long enough and come to get rid of racism the idea of a cruel all around horrible god and things that are generally accepted to have better more fair views.
"Stupid" people and "smart" people are both equally capable of either over-thinking things, or not thinking things through. There are plenty of "smart" people who tend to complicate simple issues, and there are plenty of "stupid" people who don't use critical thought enough. Finally, blindly accepting any information is possibly the stupidest thing that a "smart" person can do.