Folk songs and Art song and music are branches of the same tree. I think the argument is about style. Personally I don't mind Peter Pears vocals as much as the accompaniment, especially that by Julian Bream.
One of my pet hates is self indulgent over arrangement of folk songs, or any other musical medium for that matter. I loath 'Land of hope and Glory' for that same reason. Were there an acknowledgement by the Art music world, that the Traditional style of singing Folk songs is just as valid as Operatic vocalisation, I think we would not be so polarised. Meanwhile all pigs are fuelled up and ready to fly.