Here, just five brief comments from me, then lower down links to some other reading.
4. Ultra-left reaction: If you say that the fact that EU free movement objectively discriminates against free movement from beyond Europe, and therefore we should abolish it, either you're living in a fantasy world (because abolishing borders, however, desirable, is not on the political table in the near future, and will be even more off the table if we Brexit, with xenophobes ascendant and emboldened) or you're dishonest. We need to defend the rights we already have, even as we demand new rights too. To advocate reactionary positions (strong UK borders) because existing democratic politics (free movement in the EU) fails to meet utopian standards is to be objectively reactionary, especially in a political conjuncture dominated by post-imperial nostalgia and far right bigotry.
5. Stalinism: Stalinism's legacy includes economic nationalism and an (anti-Marxist and anachronistic) idea of the working class as white, male, national and industrial. Stalinism should have died off decades ago, but it exerts a persistent influence, including via the Morning Star and some of Corbyn's key advisors, who play a major role in distorting Labour's Brexit position. And it has had a resurgence in social media meme culture, in a way that has spilled into Labour Party internal politics, to deadly effect.
The rest of this post is basically just a reading list of some of the critiques and commentaries that have come out about this.
Coatesy: Morning Star Tries Failed Left Populist Rhetoric against the “Political Caste” to Back Brexit (21 March, on the Morning Star, SWP and other Brexit Bolsheviks)
Jim Denham: After the giant march: where now for the anti-Brexit left? (25 March)