In a lengthy Medium post, he explained he was reluctantly leaving his bandmates to protect them.
"Who in their right mind would willingly walk away from this?" he asked. "It turns out I would. And as you might imagine it’s been no easy decision."
"At the beginning of March I tweeted to American journalist Andy Ngo, author of the New York Times Bestseller, Unmasked. 'Congratulations @MrAndyNgo. Finally had the time to read your important book. You're a brave man'. Posting about books had been a theme of my social-media throughout the pandemic. I believed this tweet to be as innocuous as the others. How wrong I turned out to be."
He said that within 24 hours, the tweet was trending with tens of thousands of angry retweets and comments.
"I failed to foresee that my commenting on a book critical of the Far-Left could be interpreted as approval of the equally abhorrent Far-Right."
"Nothing could be further from the truth. Thirteen members of my family were murdered in the concentration camps of the Holocaust," he wrote. "My family knows the evils of fascism painfully well. To say the least. To call me 'fascist' was ludicrous beyond belief."
He joked that being a banjo player, he was used to receiving plenty of abuse. "But this was another level. And, owing to our association, my friends, my bandmates, were getting it too. It took me more than a moment to understand how distressing this was for them."
Frontman Marcus Mumford, whose name is "on the tin", was inevitably dragged through the mud. "The distress brought to them and their families that weekend I regret very much. I remain sincerely sorry for that," he said. "Unintentionally, I had pulled them into a divisive and totemic issue."
He praised the courage of his band for standing by him, "particularly in the age of so called 'cancel culture'."
His apology, he said, only brought the viral mob on harder.
"Though there's nothing wrong with being conservative, when forced to politically label myself I flutter between 'centrist', 'liberal' or the more honest 'bit this, bit that'," he said. "Being labeled erroneously just goes to show how binary political discourse has become. I had criticised the 'Left', so I must be the 'Right', or so their logic goes."
In retrospect, he said he regretted his decision to apologize, which he had done to protect his bandmates and their families.
"The truth is that my commenting on a book that documents the extreme Far-Left and their activities is in no way an endorsement of the equally repugnant Far-Right. The truth is that reporting on extremism at the great risk of endangering oneself is unquestionably brave," he wrote. "I also feel that my previous apology in a small way participates in the lie that such extremism does not exist, or worse, is a force for good."
He concluded by acknowledging that any further commenting on what he'd learned would only bring more trouble for the band, which is why he made the tough decision to walk away.
"My love, loyalty and accountability to them cannot permit that. I could remain and continue to self-censor but it will erode my sense of integrity. Gnaw my conscience," he said. "I've already felt that beginning."
"The only way forward for me is to leave the band. I hope in distancing myself from them I am able to speak my mind without them suffering the consequences. I leave with love in my heart and I wish those three boys nothing but the best. I have no doubt that their stars will shine long into the future."
"I look forward to new creative projects as well as speaking and writing on a variety of issues, challenging as they may be."
His former bandmates responded on Twitter with a simple single line statement: "We wish you all the best for the future, Win, and we love you man. M, B & T."