This is my problem, really. They write lovely inoffensive songs, and are obviously skilled musicians, but somehow they stick in my ears as inauthentic and wrong. As if Ralph had stolen Ted's clothes and left the Hall pretending to be him.
I don't trust any band who put on stupid voices/accents that clearly aren't theirs when they sing.
I can think of numerous examples beyond the Stones of bands who have taken music from other cultures and made it their own, accents as well - most of British Hip Hop styles with an American accent after all. So why does Mumford & Sons bother me?
All we are is dust in the wind, dude.