"People who pay money to go to a folk performance should be aware that folk often has joining-inny bits and if they don't like people joining in the jining-inny bits then maybe they should save their moey to go to performances with no joining-inny bits."

Lets just go back to the start of the thread. This doesn't sound like a "folk performance" but rather a performance by a specialist period music band who happen to be well known on the folk scene. Context is everything