I've spent enough time studying linguistics and semantics (shades of J.L. Austin!) to enjoy the problem of taxonomy as stated by Sandy Paton (and clarified by Mike Regenstrief). "Ballad" does, indeed, have several meanings, but in order to have a philosophical debate on the problem, we need to state precisely which definition we mean when we use the term. Around Mudcat, we can probably assume that references to "ballad" mean ballad2 rather than ballad3 in the Random House Webster's College Dictionary.
"Folk music" also gets used in many ways. I grabbed the Websters New World Dictionary, which just happened to be sitting on my desk. (Lisa used it under the mouse pad to raise the mouse to an ergonomically better level for her.) It says: folk music music made and handed down among the common people--but then it has a two-pronged definition for "folk song":
folk song [after G. volkslied] 1. a song made and handed down among the common people: folk sons are usually of anonymous authorship and often have many versions 2. a song composed in imitation of such a song —folk singer
Now, while definition 2 is perfectly acceptable of folk song under some circumstances, for our purposes, the traditionalist Mudcatters will want to use definition 1 (or some further honing thereof), and once we agree on that definition, we can then ask questions about under what context a song or performance crosses the line into definition 2. But we need to get definition 1 right, because definition 2 is in imitation of referents of definition 1. It's one thing if we allow a Bob Dylan original, which is in imitation of a song from a source singer in definition 1, to be considered a folk song (definition2). But then a song in imitation of that Bob Dylan song is a second-level imitation, and we can be precise about our taxonomy--a singer songwriter who imitates a revivalist is a second-level imitation folk singer. Hence the generation who imitate Joni Mitchell or James Taylor, and think they are writing and/or singing folk songs. They are several levels removed. We may enjoy their music (or not), but when we're trying to have a serious discussion of folk song in the traditionalist sense, it's good to have a philosophical tool by which we can exclude these new songs from consideration.
It's way too late/early in the morning, and I hope I;ve made some sense.