OK, they're pretty poor. I've been a member of a gay chorus (technically a "choir" only sings in a place of worship), my job being to speak as MC & narrator, and pretending to sing with the chorus at the finale. But I did have one of the greatest moments of my life, in 2008, performing on stage during the GALA Chorus in Miami, held only every 4 years, when over 6000 GLBT singers in 147 different choruses from around the world performed for over a week of nonstop concerts. That I've written about here before and posted pics.
And my partner's sister, a retired opera singer, directs such a chorus of elderly people here in south Florida. They sound pretty good. I have no explanation for this aberration, since anybody of any age can sing well enough to be entertaining.