By DCist contributor Sarah Sherman There has been plenty of contentious debate about Mumford and Sons, whose popular debut Sigh No More landed in 2009. Fans laud their radio-friendly folk rock, praising the band’s beautiful vocal harmonies and emotional acoustic crescendos. Critics argue that the group is just an amalgamation of folks like Fleet Foxes, Noah and the Whale, the Avett Brothers and Kings of Leon, slapped together for shallow efforts at an honest, family…