Rockism is generally thought of as a modern phenomenon, particularly beloved of those who decry the shallowness of pop music and feel that real music is on real instruments by musicians who have paid their dues and worked on their chops. But the Irish Times reports that Rockism seems to have originated in 19th century Ireland. Under the leadership of the semi-mythical Captain Rock, the Catholic Rockists of rural Ireland engaged in a campaign of terrifying violence against their richer Protestant fellows, who were accused of liking disco and other inauthentic forms of music. The Rockists also believed that the End Times were about to arrive and with them God would deal out terrifying punishment to the heretical adherents of the Protestant faith.
The authorities were only able to suppress the Rockists by the most violent means - suspending civil liberties and carrying out mass executions. But the cancer of Rockism was never fully eradicated, reappearing in the later 20th century. By then it had lost its millennial Catholic overtones and could appeal to people of all religions who love music made with real craft and hate manufactured pop.
The attached image is a threatening letter sent by Captain Rock in 1842 to the then Chief Surveyor of Ireland.
More on 19th century Rockism in Ireland
More on modern Rockism
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