I guess I'd have to hear the organizer's reasons. We recently did a little thing for a local German heritage society, warning them up front that we didn't know a single German tune. They didn't care; they just wanted to give the emcee a break while lunch was served (which wasn't German food, either. Go figure).

But if somebody asks us specfically for Irish tunes, no Irish tunes, Christas carols, no alcohol references, gospel, whatever, we do our best to oblige, within the scope of our repertoire. We're not in the habit, though, of learning whole new song-lists on demand. If we might have played it anyway, fine.