"Someone sat down and decided the story, the theme, the moral - and then composed words and melody to carry it"
Wouldn't open that can of worms if I were you Tom.
Group composition is still around as a theory. Gummere propounded the theory that ballads were composed 'by the dancing throng' - certainly happened like that in Finland.
My late neighbour used to bring me scraps of paper from his attic which he and his friends had made during a drinking session - one of the best of these was of a local character nicknamed 'The Drunken Bear' who went on a pub-crawl through all of the 21 (then) bars in this town and was barred out of every one of them. The elderly locals still remember the man and the incident; nobody remembers who composed or even started the song.
Unlettered Travellers were still making songs up to the mid-seventies; notably the 'made match' one, but many more - not an author in sight.
One song sung to us by a Clare man living in Deptford, about the Irish Civil War was made in the singer's presence by four men standing on the corner of the street the day after the incident; again, no author available.
First verses or even lines of some songs were made and abandoned, leaving others to finish them.
The fact of not knowing the authorship of folksongs is part of their uniqueness.
Jim Carroll