"because we can f@ck about with the words and tune of a copyright song as much as we like as long as no one catches us"
Still not ours PFR - it remains identifiably somebody's.
I can be made a parody, in which case it can be said to be folk, but even that is dodgy - how many legal quibbles have there been about tunes being filched
But even if that were the case - that is not what is being argued for here - people are arguing basically that any song they care to name can be folk because they care to call it that.
It is a small group of folkies who are attempting tp de-define something 9 haven't come up with a redefinition yet - someday, if we live long enough maybe)   
Jim Carroll