There's a difference, I believe, between singing a song as it was written -- if it uses regional words and accents -- and singing all songs in a "folk-voice". Whatever that may be according to fashion.
For example -- here in Australia I've heard the fashionable "folk-voice" change over the years. In the 60s it was an A. L. Lloyd voice. Now it's fake Irish.
I've often been asked why True-love sings with a "fake American voice". To which I say, "Because he's American". Strangly enough I've sometimes got the answer, "Well he's Australian now and he should sing like one!" By which they mean he should sound Irish with a few good old Aussie words thrown in.
Funny thing performing.
Cheers, Joy