From 1965 onwards,[1] smut aligns with its modern meaning. One such example is Murray Davis' 1983 book Smut: Erotic Reality/Obscene Ideology, whose introduction states: "For many years I have been puzzled by two questions: Why does a person want to have sex with others? And why do other people attempt to stop him or her from doing so?"[2] While the book has more to do with analyzing sex itself rather than the word smut, it draws connections between smut (in reference to sexual material) and dirt (similar to the description of smut in fungi). The book references politicians' reactions to sex-oriented radio talk shows:
[they are] new breed of air pollution [...] the prurient trash that is the stock-in-trade of the sex-oriented radio talk show, complete with the suggestive, coaxing, pear-shaped tones of the smut-hustling host,showing that people in the government were also aware of the word's obscenity.
Davis is certainly not the first author to use smut to describe sexuality. He cites the 1968 novel Smut: An Anatomy of Dirt, by Christian Enzensberger as the "poetic exegesis of the nature of 'smut'"[3] Indeed, with phrases such as "Man’s twenty-sixth excretion is himself," this book engenders a more poetic writing style. Outside of novels, an early example of its sexual use was in mathematician Tom Lehrer’s 1965 song titled "Smut":[4]
Smut!
Give me smut
And nothing but!
A dirty novel I can't shut
If it's uncut
And unsubt-tle
This song, a reaction to some 1960s movements to ban obscene books in the U.S., clearly mentions that smut is related to sexually explicit stories.
[1] https://www.google.com/search?q=\%22smut\%22&tbm=bks&tbs=cdr:1,cd_min:1966,cd_max:2022&lr=lang_en.
[2] https://press.uchicago.edu/ucp/books/book/chicago/S/bo5964295.html.