Oh dear, and I was trying very hard not to be nationalistic - I really don't know enough about American trad. song to know if harmony singing is appropriate or not.
Yes, I do come from a little country (England) and, no, I don't think it's better than any other country (although, as an Englishman, I believe I've got much to be thankful for). What I do know, though, is that my ancestors, although they were often poor and often had very little, left behind a beautiful legacy of traditional songs and I want to hear those songs presented in the most appropriate way possible. This has nothing to do with having a tin ear - I hope!
It has always seemed to me that everyone who encounters the old songs immediately wants to convert them into something else - often before they have even begun to grasp their essence. Thus the Edwardian collectors wanted to turn them into classical music whilst the 60s rock generation wanted to turn them into rock songs; to sing them in harmony is, to me, merely part of the same phenomenon.