"black is white."
No Steve, in the case of most musics they will argue black is black and white is white.
"but we have to accept it when terms come to have a wider meaning,"
As I pointed out, this isn't the case here, rather than re-defining the term and understanding those meanings, the argument is that there should be no definition or meaning whatever.
In some case language evolves; what has happened to "folk" is that it has either become a dustbin into which you bung everything you don't have another word for or it is used as a 'wannabe' term - "a word means what I want it to mean".
I seem to remember reading that you are a teacher; do you start your class by taking a vote on what you mean by say, algebra, or biology, or trigonometry or religion or whatever..... or do you explain what the word means (if it isn't already understood) and work from that basis?
Communication can only work in generally accepted terms, otherwise all men become islands.
With folk, you have the added complication of related subjects; folk-lore - music - dancing - tales - speech - art - costume.... what do you propose, a Unilateral Declaration of Independence from all of these?
As MtheGM pointed out, the term 'folk' dates back to 1846 - it wasn't a randomly chosen word, but was picked for a whole bunch of specific reasons and came with numerous social, cultural and historical implications.
If anything has altered to make those reasons no longer valid, then pick a new word; otherwise it's a definition we're stuck with - for the foreseeable future at least - virtually all our 'folk' literature adheres to the long accepted definition.
As a researcher, you really should be aware of the necessity of precision in the use of language to facilitate communication.
Jim Carroll