> But if I asked if they knew 'Barbara Allen', immediately they knew exactly what kind of song I was talking about.

Because the words "Barbara Allen" have a clearly identifiable reference for everyone: you know the song or you don't. And you have an opinion about what songs are "like it."

The word "folk," however, has no such clear reference.

It is useful - for specialists - to prescribe one. But prescribed meanings that carry no consequences for misuse are impossible to enforce.

One consequence, in this case, might be ridicule from professional
folklorists. But as we've seen, not even they agree on what they want to talk about when they want to talk about folksongs.

A very small group, on the other hand, like the folksong societies, can certainly enforce their specific usage on members - but the general public will continue to ignore them, just as it ignores the microbiologists.

The technical definitions of "virus" and "folksong" (to the extent that the latter has one) are just too obscure and complex for the average uninformed and uninterested person to care about.

And everyone around them is using the words just as they do.