I had a moment of illumination myself this evening. Look at it from the point of view of the aspiring singer - assume for the moment that he/she is a really good aspiring singer, talent in the raw, a mute inglorious Milton & so forth. If you're this singer, what do you want? Obviously you want encouragement. You want to be told what to do and what not to do - possibly including not doing some things you now do - but you want to get the news in an encouraging way: e.g. "that's great, but have you thought of not putting on a fake Tim Hart accent?" You don't want to be told you were buggering up the song, because that would knock your confidence horribly. In other words, you won't get anything useful from being told you were buggering up the song - even if you were.

So the best way to deal with (potentially) good singers is to encourage them, even when they're not doing terribly well - if you discourage singers-to-be, by giving them full and frank feedback on their perforamnce, they will never develop into the singers they had the potential to be. The best way to deal with no-hopers may be to be brutally frank - but how do you know when you're listening to a no-hoper, as opposed to a singer-to-be having an off day? To be on the safe side, it's best to be encouraging to no-hopers as well.

In short, I think we should encourage everyone: it'll help the good singers develop, and it won't make any difference to the no-hopers - they'll just bumble along whatever you do.