Good question. Sometime after 1900, because in the 19th century people were tuned in as hell, even without radio. Incidentally mandatory high school became a highly regimented thing people did around the turn of the century..
In the 19th c. people were illiterate at very high rates.
Just read something that reminded me of this conversation -- "When Tom Paine’s The Rights of Man was published in 1791, his insurrectionary defense of the French Revolution sold more than 50,000 copies in England and Scotland in the first few weeks. Given that most adults were barely literate at the time, the number was extraordinary. Over the decade, Paine’s work is said to have sold an even more unheard-of total of more than 1.5 million copies." From a biography of Ken Galbraith. What's neat is that every time I read historical writing about 18th and 19th century America I am provided with more examples of this phenomenon of massive political efficacy, especially manifesting itself in wide-ranging reading. I wonder if, back when literacy was unusual, the ability to read was taken less for granted -- so that if you had it, you used it, or felt foolish in the same way that someone who buys a car and doesn't drive it should feel foolish. Else how do you explain ... 1.5 million people. In 1791. That's like, a third of the (US) population, or more if you account for slaves who were a) mostly illiterate and b) not generally allowed to read even if they could. Anyway, that's my rambling for the evening.
I'm going to put this more clearly because apparently people think what you said was a refutation of what I said. In the 19th century, people who knew how to read (most) did. In the 21st century, people who know how to read (all) don't. That's what it boils down to.
Well yeah I was thinking of percentage of literate people who read, because that's the relevant way to compare centuries. Lot of people also only had one book (Bible) but those that had the opportunity paid way more attention than any other time of our history.