"A dumbfounding endorsement of fascism," one person tweeted in response. "Shame, I really liked that one song a while ago."
"I may be naive, but 'Banjo player from Mumford & Sons Comes Out As Nazi' was not a headline I foresaw...," another shared.
Added one: "This is so damn disappointing and really reinforces all the bad stereotypes about what it means when you hear 'the sound of banjos.' Supporting fascism ain't a good look."
Since Marshall's tweet, some have responded to older messages on the British folk rock band's official social media accounts, calling for the group to remove him from their lineup and pointing out the potential consequences his tweet may have on Mumford & Sons.
"Unless you kick @winstonmarshall out of the band, I’m done with ya’ll," insisted one fan on the band's Instagram account.
"Your banjo player is a fascist. What do you think this is going to do to you public image? You guys screwed up. Fire the fascist," demanded a Twitter user.
"Mumford and sons is about to see a lot of lost revenue bc of Winston’s insane right-wing conspiracy views," noted another. "Americans don’t want to hear the views of a uneducated conspiracy theorist and we won’t support it."
Billboard has reached out to Mumford & Sons for comment.
Per a Los Angeles Times review from February, Ngo in his book downplayed the murders of Heather Heyer (killed while protesting a white nationalist rally in 2017) and teen Trayvon Martin (killed by George Zimmerman in 2012); called the Proud Boys -- which the Southern Poverty Law Center has designated a hate group -- simply a "pro-Trump fraternity"; and described the Jan. 6 insurrection at the United States Capitol -- which took the lives of five people -- a "peaceful and celebratory" gathering. The L.A. Times called the tome demonizing the anti-fascist movement "supremely dishonest."