It’s reasonable to assume that 11% of the adult US population is still illiterate [1]. I know this is not unique to the US, and that these people may very well be as happy as anyone else. Still, if we sometimes point out that HN is a bit of a bubble, well there’s a big bubble I can’t wrap my mind around well into the 21st century! I would certainly be surprised if an illiterate person made heavy use of the Internet (though I’m sure there are edge cases, as always).
[1] https://nces.ed.gov/naal/kf_demographics.asp