Alternatively, is the act of singing without accompaniment now frowned on by the folk establishment?

There are clubs where you won't get to sing if you don't have a guitar.

AT one song circle I used to frequent there was a woman with a beatiful voice who complained of the same problem. So every now and then just for fun (or if I didn't know the chords) I'd put my gutar down and sing unaccompanied. It is something we should all do from time to time to improve our singing.