"Language has a function. And if one can take a word and make it mean anything one wishes, then that function is compromised."

I agree- to a point. Language evolves. It is not a matter of MAKING a word to mean anything that ONE wishes, but it is how PEOPLE evolve a word to take on new meanings.   

I do not agree with rigidity that prevents or stands in the way of natural changes in language, music or culture. Sort of like "not seeing the forest for the trees". Imagery and symbolism require a flexibility.

When it comes to a phrase like "folk music", it becomes obvious that there is more than one ACCEPTED definition. People can piss and moan, but that does not change reality. Arguing over what bin to put the music in loses the beauty of the music.   To say that we need a definition in order to attend a concert defies logic in my book.   Take a look at concert listings for any type of music. How much detail do we need?