Maybe people aren't so non-religious as they seem. I see a lot of claims in here that there are no believers in church choirs etc. At best that's wishful thinki

Maybe people aren't so non-religious as they seem. I see a lot of claims in here that there are no believers in church choirs etc. At best that's wishful thinking, at worst it's maybe even a lie to draw people in. In my experience, most groups that have Christian hymns in their repertoire are closet Christians at least on average. Even in the choirs that sing strictly secular songs, believers are overrepresented just from selection effects, since they sing a lot more. But yes, there are choirs that stick strictly to secular repertoire. There was a "red" choral revival in the 70s, and of course worker and patriotic choirs go a long way back. They got to have something that unites them besides the singing, though. In my town the main secular choirs are the opera choir, which is united by their love of opera and classical music, and the chamber choir, which is 90% doctors and nurses from the local hospital.