Derpist, I wonder if its the case that basically anything that smacks of nationalism, even if driven by a huge working class vote and against the clear wishes of most of the wealthy, will now spark this strident opposition.
I think this has always been my problem with left-wing movements. You can't beat something with nothing. They may have a great deal many flaws, but things like traditional civic society (whether it be local community, religion, or inclusive nationalism) are some of the strongest constraints against powerful economist interests. So you have leftists who want to tear down those things because of their flaws...and they inevitably find common cause with corporate interests that want to tear down the last barrier to their unlimited control of society - and the two groups just meld together after a while because of tribalism and political polarization and stuff.
The only person who I thought made a good argument for Remain was Jeremy Corbyn, but his voice just got drowned out by the media narrative that everyone who didn't like the undemocratic, austerity status quo was some sort of racist and that you had to bend the knee or be punished by Ramsay Banker.