" ... if somebody's singing off-key, do you think it's a good idea for another singer in the singaround to go up to them and say "it's a shame you were singing off-key"?"

Here's a thought! Perhaps someone who attempts to deliver some criticism is actually braver than the singer who stands up in front of an audience and sings off key - especially given the un/anti-critical attitude which tends to prevail in many folk venues today(?)

Of course, it all depends on whether the critic was genuinely trying to be helpful or was just delivering a spiteful put-down ...