I think it boils down to horses for courses. If the singer and/or the song is an obvious solo performance then it would be very rude of the audience to join in without permission. On the other hand if I was to sing a shanty and no-one joined in I would be a bit put out! What we need is a modicum of common sense. Something that does not seem too common unfortunately:-(

Something did just spring to mind as I mentioned shanties - At Lancaster some years back a fellow mudcatter upset quite a few people by joining in with not only the choruses and refrains but the verses as well! The general concensus (sp?) was that the audience had paid to listen to Johnny Collins (as it was) NOT an unknown and very loud participant! Common sense again. Join in when appropriate and listen when it isn't!

What is difficult about that?

DeG