You never tell people they're no good, you encourage them to improve, and the only way they'll improve is work - practice, call it what you will. If they practice and don't improve, then you help them; if they still don't improve they have a problem, but it's their problem, not yours, and certainly should never be your audiences'.
When veteran singer and musician Packie Byrne found he could no longer sing he polished up his storytelling technique - last time I saw him he was still going strong. It's a little like the Monty Python sketch about the one-legged actor applying for the role of Tarzan - perhaps that's not what they are best suited to.
I think the most outrageously reactionary statement I have ever heard about singing is that we should hold back our better singers for fear of upsetting the mediocre ones - Jay-sus - talk about roll over Beethoven!
As for technique versus involvement; MacColl summed it up perfectly for me in an interview:
"Any art form, whether traditional music, painting, or whatever, must provide a challenge for the people who work in it, otherwise it dies." "The main objective for the singer is to create a situation that when he or she starts to sing, he or she is no longer worried about technique; they have done all that and can give the whole of his or her attention to the song itself; to the sheer act of enjoying the song."
Jim Carroll
PS countess - I'm afraid he wasn't being ironical