Boy, turn my head for a moment and a thread grows up...

emily, don't be appalled by what Peter Yarrow did. You don't know the reason. It could be as simple as, with a song like Puff, where so many of their audience knows it, they cannot hear each other when they sing. That's a pretty important factor for a group. My response is that he probably had a pretty good reason for asking and IO'd give him the benefit of the doubt.

One way I deal with unwanted accompaniment issues is to put a guitar on my knee, strum it a little and then launch into an a capella song while muting the strings, essentially using the guitar as a prop. You don't have to play guitar to do this. Mary, just ask to borrow a guitar from a neighbor and then don't play it. You'll make your point.