"If your only criterion for performing a song or tune is whether you like it that reduces folk music (or other the form of music of your choice) to mere entertainment." (Richard Bridge)

But folk music always was entertainment. The role of the traditional musician was to provide songs and tunes to entertain his community. Why do you dismiss it as "mere" entertainment? If its not entertaining then it becomes a sterile academic exercise. Entertainment doesn't have to mean frivolous.

Performers who earn their living from it may have to tailor their repertoire to the tastes of their audience. For the rest of us, why perform something if you don't like it? For me, a song or tune has to touch me in some way. Regardless of its provenance, if it doesn't do that then I won't learn it.

As for stylistic choice, it is style rather than content which for me defines national music. A tune such as "Flowers of Edinburgh" is found throughout the British Isles, but the proverbial Englishman, Irishman and Scotsman will all play it differently, with distinctive regional styles (which extends to the way variations creep in as well as playing style). A visiting American will play it differently again. It is the style which distinguishes one version from another of what is essentially the same tune.