"Only rules are there are no rules",

Shimrod, I think you know very well what I mean! My whole argument is that in singaround/session environments each performer has the right to perform in whatever way they like without people like you telling them this isn't right or that's not acceptable. However, I would concede that any Guest artist who is being paid, and entrance fees being charged should take the trouble to learn their material. If they don't your answer is simple, don't go to see them.