"what is it that Jim and Jack Blandriver are arguing about?
it seems to me they agree with each other - why are they being nasty to each other?"

Too much nastiness hereabouts from all sides, if you ask me. I've had robust exchanges with Jack B in the past, but we meet as friends when we bump into each other at festivals, and the same goes for you, Al. Jim and Jack B both clearly enjoy and value traditional singing, and both realise that 'Tradition' and 'Revival' are different beasts, so their argument is about the baggage rather than the actual music. But then, the most acrimonious disputes are often those between passionate enthusiasts for the same cause, so perhaps it's not surprising.

I disagree with Jim in his defence of the original meaning of 'folk' (long lost, IMO), but I respect his argument, and his first-hand accounts on this thread have been fascinating reading as always. Mudcat would be much poorer without his contributions.

As for Musket's "old asthmatic lass from a caravan", I suspect he's talking about Caroline Hughes, a CD of whose singing I recently had for review. I daresay most people would indeed pass on by, but the more I listened, the more I got out of it. Which is a reflection of nothing, apart from different tastes.