whatever people truly prefer is up to them of course..but if you have a core of good singers, would you not want to hear them sing with each other more than listening to one person? that is my preference. I used to go why aren't they singing along with me...surely some know this song. and what is great is when several people know the song but not everyone..and good singers generally tone themselves down and follow the leader..sometimes the leader really needs help though and the group could support her.

but there is no all over rule that it is rude to sing along. It was the standard american practice, at least where i am from. Let's sing something we all know...it was never let's listen to this person, then that person, then the next person. Poor voices are not helped by this custom and good ones are silenced more than they need to be...but really, whatever the group and the singer wants but don't be bullied into something.