Returning to my 'singer's backstory' angle for a moment, Anne wrote:

"I'm not sure that there was any explanation behind Jeannie Robertson's version of 'Son David', but I am sure that it was a very significant song for her, because her only son had died young, so her memory of loss was very strong. (Apologies for not taking the time to check this just now, but will do later, and if there's any further info. - I'll post it.)"

I've now found the snippet I was thinking about, and (like the 'Unquiet Grave' example I mentioned) it's in Atkinson's 'The English Traditional Ballad'. I was wrong in thinking that Jeannie claimed any personal connection with the events in 'My Son David', but she did give both Herschel Gower and Alan Lomax a detailed description, in the most everyday language, of the motivation behind the ballad, in which 'Son David' was merely defending himself against his jealous younger brother, and killed him in a fight. No hint of the folklorists' 'incest' theories in her account! Despite the absence of any 'friend-of-a-friend' connection, it's interesting that the singer provided such a detailed rationalization of the ballad she sang - if nothing else, it's another demonstration of the singer getting inside the ballad tale.

And going back to how we sing them, I explained above why I'm sceptical of the 'let the song sing you' school of thought, but I do think Crow Sister is on the ball with:
"I'd suggest that [ballad singing] requires gentleness and humility. Being not so impressed with your talents that you end up using the the song merely as a vehicle for a display of ones vocal and instrumental expertise."