Rapid keyboard composition for organ dating from the baroque period
Fans of classical music absolutely despised them (sometimes) for "butchering" various well-known pieces in their attempts to interpret these standards in a rock idiom.
No, what distinguished ELP was the amount of venom spewed upon them by other "high-brow" artists and their various followers.
Such symphonic centres – London, Paris, Mannheim, Milan – often had an outstanding orchestra, a flourishing music-publishing industry, a ruler with an intense interest in music, or music-loving patrons in the form either of courtiers and their hangers-on or of a well-to-do middle-class and aristocratic audience.
Salzburg fell somewhere between the extremes represented by Rohrau and Mannheim: it was one of a number of lesser cities and minor courts where the symphonic tradition was received from elsewhere and cultivated assiduously.
Regardless, however, this is a perfectly legitimate statement on the general level.
Fans of punk have always detested them as they would any prog band, but this extended far beyond normal levels of loathing; as an example, one of the staples of late 70's Sex Pistols shows was to burn life-size statues of Keith Emerson in effigy (or so the legend goes, and I really hope it's true because it's a hilarious legend).
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Or maybe the older generation was just mad about all these young whippersnappers infiltrating their societal niche ....