Kerouac and his fellow beat generation writers viewed the term "beatnik" as perjorative. The term was coined by Herb Caen in an article in the San Francisco Chronicle on April 2, 1958. Writing close on the heels of the Sputnik episode, Caen's addition of the Russian suffix -nik was likely an effort to portray the beat generation writers as un-American. Beat poet Allen Ginsberg wrote to the New York Times, deploring the "foul word" (Wikipedia).
Nevertheless, from there the media took over, stereotyping the "beatnik" as a beret-wearing, goatee-sporting, bongo-playing, poetry reading counterculture character.
Or as criminals.
And the ignorance continues today. Note the incredible wikiHow titled How to Be a Beatnik Stereotype. Someone with more time on their hands than I might want to edit this particular wiki.
Jack didn't wear berets, sport a goatee, or play the bongos. Yes, he wrote and read poetry, but comparing the beat generation to Bob Denver's Maynard G. Krebs character on The Many Loves of Dobie Gillis is ludicrous beyond words.
Consider Kerouac's own words from a November 22, 1960 letter:
The vision of America is being destroyed now by the beatnik movement which is not the "beat generation" I proposed any more but a big move-in from intellectual dissident wrecks of all kinds and now even anti-American, America-haters of all kinds with placards who call themselves "beatniks."*
Or this from a February 15, 1961 letter:
"Original members" of the Beat Gen. means it started out in 1948 as a group of poets, beardless, with no political beefs, no idea of "nonconformity," just poets. Today's "beatnik" cant even recognize Stan Gets [sic] when he hears him, or even tell the tune he's playing, etc. "Beatniks" are Henry Wallaceniks jumped on the movement for left-wing reasons. I am a Catholic Conservative.*
In later years, Jack even distanced himself from friend Allen Ginsberg over the latter's anti-war sentiments that Jack thought were un-patriotic.
Bottom line: please don't associate the term "beatnik" with Jack Kerouac except to de-mythologize its inappropriate use.
*From Jack Kerouac: Selected Letters 1957-1969, edited by Ann Charters.