Tootler,
I can't disagree with any of the points you're making, nor do I have any quibble with your list.
Unfortunately the opposite all too often happens here.
Over Christmas we had two magnificent sessions ruined by a visitor with cutlery (don't know if you've heard Con Fada's 'Spoons Murder - she was a prime candidate for te Raleigh bike).      
Last Summer we had another lady with a tambourine, one of those with jangly bits (the tambourine, not the lady) who sat there and thumped it completely out of time. The locals said nothing - it took a fellow blow-in to tell her to desist - to which she replied - 'I thought that's what you were supposed to do'; she then disappeared in a cloud of huff.
Cap'n, have far too few teeth left to waste them on Comhaltas.
Jim Carroll