I think one of the wonderful things about human voices is that, no matter how apparently discordant, they can blend and make those harmonies acceptable to the ear where using those same harmonies with instruments can make many people squirm! I can certainly listen to some of the more modern classical composers' compositions for a cappella singing, and really relish the harmonies, but hate those same composers' instrumental pieces.

Having said that, I'm not keen on 'clever' harmonies in folk songs - I believe that they tend to detract from the words, which IMO is the most important aspect of folk song. Contrapuntal harmonies to folk songs are I think, 'unnatural', and those that are 'instinctive' are more likely to get the words across. I didn't always think that way, but I cringe now at some of the 'written' arrangements that I used to sing!

Oh, and the 'get off my note' syndrome makes for some hefty bruises on the upper arm from the next singer's elbow!

Barbara