I have a particular lack of agreement and respect for the "all music is folk music" opinion.

The problem is that the definition of 'folk music' lies somewhere between that, and "no music is folk music" (I don't know of anyone who holds that latter opinion, but some people's definitions come pretty close to it :-)). Each individual peobably has a different idea as to where in between these two extremes the definition lies.

And that's the problem. Each person thinks their definition is right, and everyone else's is wrong. So the question cannot be answered in a way that would satisfy everyone.

Proving Fermat's Last Theorem was a piece of p*** compared with this :-)