Sandman, what is being discussed seems to concern an event at MT club many years ago at which neither of us were present I think?
'Apparently' really isn't good enough, is it?   he said... she said
I am well aware that Bob can be an intolerant listener but I've been there when singers & musicians have thoroughly deserved such treatment, more often for condescension and pseudo academic introductions to songs & music sets than for poor singing/playing. I wouldn't have the nerve but have often felt sympathy in an audience for what he said/did.
I have heard some VERY eminent 'source' singers talking during songs & even more in music sets, and that's not a crime, unless we want our music of the people delivered and received in silence?
Apart from this, I agree with all you say about rules, but I really don't think you are living in the real world!
This is not knocking folk clubs and sessions, I'm very grateful to the platform they continue to give me!