I find the definition of 'bad' difficult. I can understand 'BAD', but I've not encountered many of those.

(Into Grumpy Old Man mode)

There seems to be a concentration today on polished performance - understandable, with the plethora of media currently available. It didn't used to be like that. In the second half of the 60s and 70s, I was one of the organisers of a successful club, meeting every Thursday evening. Usually we had about 50 or 60 in the club. We booked a guest about 8 or 10 times a year - those evenings were more concert performances than club nights, although occasionally the guest would only do the second half.

The normal club nights were filled with about 20 members, mostly solo or duo, doing short spots of 2 to 4 songs and a very few instrumentals. We also had another dozen or so from the surrounding area, who would drop in from time to time. The standard varied widely, from a few who took paid bookings and have subsequently recorded and performed on major stages, through the majority who were reasonable singers and could hold the audience, to a few who struggled.

They weren't BAD singers, or even bad singers, but they lacked either the confidence or the voice to hold the audience. We usually restricted them to one song. Some of them developed into competent performers, while others gradually faded away.

Starting this thread, DeG said: I believe that everyone should have somewhere to sing or play, regardless of ability. But I would restrict the bad performers to performing within a circle of friends and try to help them improve that way. I would not, as a folk club organiser, let them perform in front of an audience of strangers.
We had a folk club, mainly attended by regular members. That still seems to me the right place for aspiring or developing performers. I'm sure I'd feel at home in Burnley Folk Club, but it's a long way to go.

I think the other factor that helped was that we had no amplification - what we heard was 'real'. As to where 'bad' singers can go now - they could always join the rest on the endless TV shows, where flashy production and fancy electronics can disguise a lot of faults.

(Grumpy Old Man mode off)

I would distinguish folk club nights from concert nights. If you're advertising a performance, it's not appropriate to include singers of much lower ability. But for 'club' nights, I would accept almost anyone who is brave enough to try. I only rejected one volunteer in 10 years - he was rolling drunk. I still wonder if I might have missed a memorable performance!

Phil