The belief that intelligence is a heritable trait is a core tenet of eugenics, and is the very basis of the setting of Idiocracy. In the film, corporate capture and the gutting of the US government via bread and circus tactics didn't create a "stupid" society; stupid people overbreeding caused a societal drop in intelligence, which then created the issues. The film gets cause and effect backwards, if only to adhere to the eugenicist pretext.