"Volgadon - traditionally congregations in England generally sing just the tune"

Which tradition is this? If you mean that this is the way congregations sing NOW, how is that more traditional than the older, West Gallery style of church singing which is full of harmonies?

The fact that RVW only notated the tune does not mean that this is all he ever heard. I believe there is evidence that some of the tunes he collected were, in fact, originally sung with harmonies; because of his own bias, perhaps, he chose only to note the tune, and then, when orchestrating the music later, sometimes added harmonies of his own.

There has been speculation (notably, I believe, by Karl Dallas) that it was often the bias of the collectors themselves - Sharp in particular possibly setting the precident - which caused the songs to be collected largely unaccompanied and without harmonies. Later collectors find a significant amount of musical accompaniment, and later recordings of singers in pubs (not revival singers) definitely contain spontaneous harmonisation on the choruses.

You still haven't answered Woody's questions 2 and 3: HOW would you enforce your cultural apartheid?