I think part of the problem with this thread is that we are muddling folk clubs, sessions and morris side sing arounds - different animals I think.
Folk clubs - with membership lists and paid performers and entrance fees - have their own rules about who should perform. If you don't like it then do one of 2 things - join the commitee and change it from within or don't go. Its hard enough to run one of these - and a big time committment. You have to admire the organisers even if you disagree with their choices.

Sessions are a bit different I think - and perhaps guest bob this was what you were refering to. For me, a session is about what you can add to the do. I have my own mark scheme
perform for others to listen to                         1 mark
perform so others can join choras                      4 marks
perform so others can play, join both verse and choras 10 marks.
Any other views
FloraG