"...the most repressive attitude toward music itself that I've encountered involved a small denomination that allows singing, but with no instruments;"

As a person who grew up in such an environment, FP, I don't agree that singing without instruments is repressive. Today I most definitely prefer instruments for most songs but in those days I distinctly remember the awed chills down my spine that the unadorned voices caused me.

I might contend that singing without instruments helps the 'ear'. The organ may have been designed to help people stay on key.