Don't have a problem with people singing traditional songs which are recognised as 'belonging' to regulars, otherwise you are assuming that the door of your club/singaround is never going to be darkened by a stranger who is not aware of the regulars' repertoires - bit cliquish, don't you think?
On the other hand, I witnessed an incident where a well-known guest was booked at a club and one of the regulars opened the evening by singing (rather indifferently) four songs which were widely recognised as having been introduced into the revival by the guest (two traditional and two penned by him).
The guest said nothing, but proceeded to open his spot with the same four songs (magnificently sung).
Never sure of the etiquette here, but I know who won that particular 'flighting'.
Jim Carroll