"MacColl wrote and let the people (Folk?) decide. And they did, and do."
The vast majority of people don't give a rat's arse what the songs are or where they come from - they sing them because they like them.
Because they sing 'You'll Never Walk Alone' on the terraces doesn't alter the fact that it is a Rodgers and Hammerstein composition and will never be a folk song while it has a hole in its bottom.
Repetition or admiration does not make a folk song - the genre is much more complicated and important than that.
Jim Carroll