I've come up with a fair and just solution to this whole dilemma:

A new singer turns up at a singaround, right? After three months the organiser, after discussing the matter with the rest of the group, takes him (or her) to one side and gives him a fair appraisal of his singing . The newby is then warned that he must improve or else. After six months the process is repeated. If, after nine months, there is still insufficient improvement he is frog-marched out into the car park and duffed-over. At the end of a year if the newcomer is still boring everyone shitless, reads his songs from an old note-book, is excessively irritating, can't sing in tune, or has not built up an interesting repertoire etc., etc. he is duffed-over again and then expelled from the singaround.

What do you think? I think that my scheme should do wonders for the general standard of singarounds!