If they don't want people singing along they should certainly say so right up front, preferably when the performance is advertised and tickets are sold. Some people will like it. Some won't. To each her own...the musicians are of course free to set it up how they like it but I would assume the default is to sing along in the chorus. Some cultures are more shut up and listen to the singer and some (many Americans) are *** you probably know how inclusive I am of who wants to be an American..join in the nomenclature if you want***...are more "let's sing something we all know" and are more asuming that you will join in. But if you are in your own homegrown culture and that is the norm to join in, then join in unless told not to and then decide if you want to attend a performance under those conditions again. mg