I can see both sides of this.
I've been in community choirs (for adults) where everybody is welcome - auditions for solos, as you'd expect - although I always remember one where there was a woman with the double whammy of being a terrible singer but convinced that she was amazing and insisting that she stand right under one of the microphones, so the tech guy just switched that one off!
Yes, a good choir leader can teach people to improve, within reason, but there are people - often those who insist on singing at top volume - who are just tone deaf and cannot/will not be helped, and who will single-handedly wreck the choir.
I don't know if anybody on here has seen the guilty pleasure programme 'I Can See Your Voice'. The basic premise is that contestants have to pick up on cues and clues when people mime (good ones mime to a recording of their own voice and bad ones mime to somebody else's, who IS good!) and guess whether they are good singers or bad singers - and they win money if they identify the good singers and the bad singers win the money if they can fool the contestants into thinking that they are good singers!
They usually avoid those who are mediocre and only have wonderful or horrendous singers - and the horrendous ones know that they are awful and think it might be a laugh and a good earner if they can wing it - but I always thought how extremely awkward it must be if the programme makers approached (or were approached by) terrible singers who genuinely believe they sound like Adele or Lewis Capaldi, when they actually sound like a cat with its tail trapped in a door!
Obviously, there are ways of telling people who sound terrible sensitively, but it's difficult when faced with those who refuse to listen and gainsay you when you tactfully try to tell them that they are good at a lot of things, but maybe singing isn't one of their fortes.
As has been said already, it's accepted that people are chosen/accepted on merit when it's a sports team, but it's often considered really cruel when it's a choir - even if somebody has such a frightful voice that drowns out the others and makes the choir into such a laughing stock that there's no point anybody else trying or even turning up.
It seems very unfair on people like me, who were the last to be picked for PE every single time (oh, the grimaces of sheer disappointment on the pickers' faces, who would rather their team have been one player down than have me), but who have quite good voices and have even on occasion been picked for solos.
It's a difficult one - especially when you often hear proclamations that 'absolutely anybody can learn to sing well', when the truth is more like 'most people can learn how to sing better, but some are thoroughly beyond all hope, however hard they may try'. Maybe it's also a significant factor that sports teams usually have a set number of people, so people can understand that they weren't one of the best seven (or whatever) players this time - but they were almost certainly the eighth best by the narrowest of margins(!), and can still make it on to the subs bench (which they never leave). In sharp contrast, choirs don't usually have a set number of people, so you can't use the excuse that "You're really great, but we already have X number of people who are just a tiny bit even more polished than you at this stage".