I suggest (not my place to insist anything) that people be asked to reach a standard (tune/words/interpretation) before they sing publicly - for the sake of the audience, music, and for their own self-respect.
I believe that anybody can reach a basic standard with some work - surely it is not unreasonable to ask that that work is done before they become ambassadors for our music.
You're doing it again Richard - who mentioned 'masters' apart from yourself?
Jim Carroll