Quote: "But nowadays concerts (away from festivals) attract a whole cohort of people who wouldn't dream of going to a club or a festival, and are not familiar with the idea of joining in"...
Or conversely, specifically go to concerts rather than clubs because they are listeners not participators and are actually consciously trying to avoid the joiners inners!
Look, you lot (the folk club folkies) have got your extensive network of venues where you set the rules. There are many of us who like folk music who don't tend to go to folk clubs because its not our scene, or who go to folk clubs for one sort of experience and concerts for another.
What I know is that if I pay a tenner or more to see an artist, I don't want someone sat next to me belting it out: I didn't come to hear them or pay to hear them! Wanting to get what I paid for does not mean I'm missing out on something - or should I say it doesn't mean I'm missing out on something I want.
What I suspect the problem is is that some folk club folkies think they have special privileges and sole ownership of folk music in all contexts. This means they think their rules of etiquette should apply to non folk club venues, and the rest of us, who haven't paid our dues at the local folk club for 40 years should shut up and put up.
I therefore salute the opening poster for not doing this. Just as I wouldn't take my hammer and chisel to a sculpture exhibition and try to "improve" the exhibits... Conversely, I may take them along to a sculpture workshop or club...