The closest historical parallel to the "you can't possibly be autistic" attitude can be found in the slaveowners of the American South, who passed laws making it illegal to teach slaves to read and write. Then they arrogantly insisted that essays written by black abolitionists had to be fraudulent because "everyone knew" that blacks were mentally incapable of reading and writing.
After reflection, I've decided to post my own pictorial commentary on bigoted attitudes like that. You can find it in the sidebar. And as you've probably guessed if you're a regular reader of my blog, it's not a collection of cute little baby pictures. Enjoy.