The left has always had a strong anti EU faction, the likes of Benn and Shore, Foot and even stood on a pro leave manifesto pledge in 1982. They saw the way the EU was heading and the EU is no friend of Socialism. Its a pro capitalist entity and as an anti capitalist I could not support it despite being in bed with the strangest of bedfellows. I despise Farage and his ilk with a passion/
The reason though it has been a disaster is because of the people implementing it, not because Brexit was inherently a bad choice,