An inability to examine an issue in depth. An inability to get beyond the basic thought, which sticks in their head like a mantra, closing off all other avenues of consideration.
Due to Larry's bumper sticker mentality, he was unable to understand the nuances of an issue beyond a basic premise, as in "guns don't kill people, people kill people." He lacked the ability to think beyond the bumper sticker.
by The Polish Grammarian October 19, 2015