Having read this thread and others like it, and having attempted to follow the convoluted logic of various and sundry people putting forth their reasons, excuses, prejudices, and quotes from presumably knowledgeable sources (??), it seems pretty obvious that the definition of folk music is essentially the same as someone's oft quoted definition of pornography: "I can't explain it, but I know it when I see it."

Let's cut to the chase here:

If you like a song, go ahead and sing the bloody thing!!.

Don Firth