I was having this conversation with my boyfriend recently. He prefers to write the words of a song down and learn them that way; I prefer to listen to a recording till I have the song. He reckons his way means you're not picking up someone else's "version" and copying their traits and mannerisms and any little vagaries they might bring to it. That's true enough, but my argument is that when people learned songs from each other they did it by listening enough times to "get" the song, and then, by singing it themselves over time, would put their own stamp on it. They were equally prey to picking up mannerisms and idiosyncracies from other singers - did that make them wrong?
I dont see how it's so very different if I learn a song from someone else's recorded version, so long as I'm not slavishly copying their style. I learn stuff from people like Harry Cox and Sam Larner, and equally from Peter Bellamy or Eliza Carthy or Spiers and Boden. If it's a good song, I want to sing it. And while I like knowing the "source" versions of songs, they are, after all, just a snapshot: one moment in that song's life and evolution, one person's interpretation.