What have you done to help those "toe curlingly awful" performers to improve?
At various times I have suggested; learning a song rather than reading it from a sheet of paper, practising it, trying to find a song more suited to the singers' voice, singing something other than a 42-verse dirge in a time-limited and raucous pub session and even taking up mime or macrame rather than singing.
The fact is, there are some people who like to sing but who are absolutely bloody awful. It's the price we pay for the 'inclusivity' of fok, I suppose. For myself, that's when I take myself off to the bar, go and have a prolonged pee or find an old mate to natter with. I'm afraid I don't do the warmy, huggy "everyone's equal in song" schtick. I get precious few opportunities to enjoy a decent singaround, and get pissed off by the care-in-the-community noodlers and mumblers with absolutely no talent who have clearly never been subject even to constructive criticism.
Yes, we all start somewhere - I started in the bathroom and the garden shd and worked my way up to singers' nights at my local folk club and it was a long time before I felt able to sing in a public session - but some folk seem to take the piss out of the courtesy of the average folk gathering.