No need to apologise, MuddleC, you've made some interesting points.

I agree that "sing something cheerful" can be counter-productive. What I find really makes me lose the will to live is the bad singer -the one who woffles on before starting, apologising in advance for how bad it's going to be; can't find the right key; too quiet; too slow; doesn't know the words and seems a bit hazy about the tune; etc etc (OK, I'm guilty of some of these from time to time, but not all of them, and not more than one in one song). Even the most "cheerful" or supposedly funny song can be excruciating when done badly, just as a song with dismal subject-matter can be truly thrilling when well done.

I don't mind at all when other people join in or harmonise, as long as they're not trying to superimpose their own "correct" version of the song onto mine.

Marje