You can argue that a "folk song" has to fit the set of criteria that has been constantly referred to - the old "oral tradition". Frankly, it is a set of self-fullfilling rules that will give you the type of song you are looking for. I assume that if you discover that someone wrote the songs that Walter Pardon sang, and it did not go through such a process, then it is no longer a traditional folk song.

"Folk music" is the process of transmitting songs and sharing within a community.

You can make a very clear scientific case that will show that Pete Seeger, the Weavers, Odetta, Ed McCurdy, the New Lost City Ramblers and others do not belong in the genre "folk music" - but what is the gain in that?