"I guess we will never know since we can't even get a consensus on what a folk song is."
We have a consensus in the form of existing dictionary definitions which tend to agree, and masses of documented and published researched information which essentially forms a core shape to what is meant by 'folk'.
The problems arise with the clubs who have decided to go AWOL and the fact that they have scattered themselves all over the musical landscape and have no definable form of their own makes it very difficult to recapture them, bring them back to base and slap them in the brig!
It makes utter nonsense of any artistic form to refuse to define it so it can never be discussed other than by acrimonious shouting matches.   
Folk song is far too enjoyable and informative to be lost to us this way.
Jim Carroll