Background noise.
Ever since the greeks began taking up writing and reading, and Socrates bemoaning the loss of the ability to memorize entire epics, there has been an attack on "vain" knowledge.
I'd guess in his mind the epitome of a learned person was the aristocratic scientist who read first sources in the native language: Sanskrit, Greek, Latin among others. First sources, always in the original, not interpreted.
I don't doubt that results in improved critical thinking. But whether it's a good investment when you have limited time, I don't know.
It seems to me the printing press actually improved things, but in more recent time the educating power and self improvement potential of books got significantly diluted by drowning books into huge numbers of published entertainment pieces. Entertainment took over knowledge.
I'd say the opposite: today people are reading less book than 20 years ago, writing on paper less and language is on a trend ot become impoverished.
They thought similar things about chess - that it would make a generation of morons.
"The Simpsons" were controversial in the 80's, since they just knew kids would try to emulate Bart, just for a more recent example. My mother wouldn't let me watch it for some years on the single family television.
And lastly: I don't know if folks are reading fewer books or not if you count digital books. That said, I think folks read a lot more than they used to, since a lot of communication is text-based.
[1]https://en.wikipedia.org/wiki/History_of_chess#Europe [2] http://www.strangehistory.net/2013/04/07/the-evils-of-chess/
What's entertainment and what's knowledge? Where do you fit Fahrenheit 451?
Getting back to Bradbury's points about TV/radio, he talked about how TV/radio addiction makes it harder to read a book.
So what? You've replaced one addiction with another. Books aren't inherently better than other media (except perhaps some ancillary stuff about your brain generating imagery or eyesight). I'm saying this as a person with this lament (more because some stuff is only available in book form).
I wonder what he would have thought about audiobooks.