People have a feeling the world is mostly made up of people just like them;
that just because everyone they know is of a certain persuasion, then everyone must be like that. They use this certainty to explain how the world is full of sinister minorities highly organized and determined to victimize them.
I learned this very young. I caught my mother once in just such a brief lapse of common sense, while discussing how Fidel Castro could gather so much support among the peasantry and the urban poor.
"There was never any widespread, crushing poverty in Cuba. Hell, everyone in our family and everyone they knew had servants."
QED.