If a family member exhorts you to come to every performance, thinks they are the bees knees and gets cross if you don't go, you have a relationship problem, not a choir problem. My mum is in a choir and wouldn't dream of making anyone go to her concerts, I go about half the time if I can make it, and so do the rest of the family as convenient, it's not a three line whip. In their case, though, even though it's an 'all-comers' choir, they are very good and I look forward to their candle-lit choir service and the like.
The bit about 'failed musicians' is laughable. Of course hundreds of choirs across the land can't all be led by semi-professional musicians, um, they are all working semi-professionally. That said, there is a huge amount of amateur talent out there, including those who have made a good living writing music and as singing teachers.
This reminds me of people who like to mock 'Am-Dram' for this reason- yes, you are not likely to get semi-professional actors or directors at your local theatre, does that mean everyone should pack up and go home? Or not put on any ticketed productions in case the standard of some of the actors (again usually open to all) is not quite as high as the West End stage (having said that, I've seen some quite bad West End stage productions, and some quite good Am-Dram ones!)
Taking part in group activities IS, however the OP is still mocking those who claim it, associated with better well-being and mental health. It doesn't matter if you go to an amateur choir, art club, am-dram production, volunteer group, ballet class/show(which are often ticketed to raise money for the hire of the hall), getting out there and getting involved and having fun with others is incredibly good for you. If you don't like watching people do this, then body-swerve the performance, claim to be ill or whatever. Most people do support their family and friends and children though when they perform in public, even if they are not at an incredibly high standard. It's called participating in life, it's really nothing to criticize.