If as professionals or 'gifted amateurs' we have no time for newcomers then imo we ain't all that professional and w'ain't all that gifted. Someone somewhere sometime gave us all a bit of encouragement, tips on how to improve, remarks that made us look at our performance and delivery. As a result we learned and grew. There is nothing wrong with passing that on.

Club owners/organizers have not only the right but also the responsibility to provide good acts for audiences. If they do not provide good acts they will be ex-owners/organizers because the audience will go away. Part of newcomers learning the ropes is them finding out if a song they intend to do will conflict with another performer who may have already decided to do that song. I listened to "I'll Fly Away" three times one evening in an hour and a half at an open mike. I was the guest act and I had the greatest urge to start my set with the opening two lines of the first stanza--I knew I wouldn't have to do more because I'd have been laughing by then.

Another reason people go to folk clubs is the ambiance the clubs generate. I don't think there's a formula for that but there are necessary actions to take. Good guest acts, organized open mike, time for the audience to speak with each other, a place for musicians to speak separate from the room, and no bullshit from anyone on or off the stage. All handled politely, of course.