whether it stems from our Puritan forefathers, who decreed secular music to be sinful, or our overbearing music industry, which pushes music arranged to the hilt, or a combination of both

I doubt if it is the first - because "we" as a society certainly haven't had any problems overturning and or ignoring any of their other strictures. *grin* I strongly suspect the music industry - combined with radio and television; public and communal singing was common into the fifties and even in some areas into the early sixties.