can't see the not joining in on the chorus bit, isn't the joining in bit what it is all about, what makes it different?. At our local session people come for a sing and it takes them quite a long time to learn songs so they want to sing the same songs, I am acutely aware that they have not come to listen to me! Also, in a non concert environment people are having a night out with friends and you cannot expect them to sit around tight lipped so, daunting as it might be for some, you just gotta belt it out and hope enough people join in to drown out the chat.