Well, capitalists(people who own the means of production) who can read generally continue to support the system that benefits them.
And they’re able to pay so proles mostly only read ideas that are supportive of capitalism.
But that isnt the point of the meme, the joke is that this guy thinks illiteracy is the best defense against communism, when the best defense is making communism into a boogeyman so literate people won’t read their ideas.