None of the reasons for opposing the EU given here are actual reasons for leaving the EU, because leaving the EU in order to retreat into a series of nation states where all of those conditions exist in spades is a step backwards. Worse than that, it suggests that the solution to all those problems is to retreat into those capitalist nation states, with the implication that those nation states are somehow better, more progressive, and that workers in each of those nation states somehow has more in common with its own ruling class than it does with foreign workers. It is not a matter of whether the British Government is today made up of Cameron or Johnson, or Corbyn or Miliband, that can change overnight. In the end, the suggestion that the answer to workers problems across Europe can be solved by a retreat in to Little Englander nationalism, or any other kind of nationalism, complete with measures to protect British capital and place the blame on foreigners via immigration controls, import controls and so on, is the same mistake that social-democratic parties made ahead of WWI.
The idea that Britain under a Corbyn or any other form of government could engage in any kind of real social transformation without the support of large numbers of workers across the EU is dangerous adventurism. It is nothing more than a repetition of the national socialist agenda of Stalin for “Socialism In One Country”. The difference is that, as Trotsky points out, talking in the 1920’s, about how any such move in Britain would be strangled by the US,
“England is an island and America is likewise an island of a sort, but much larger. England is completely dependent in her day-to-day existence on countries beyond the ocean. But the American “insular” continent contains everything that is necessary for existence and for the conduct of war. England has colonial possessions on many seas and America will “liberate” them. Having begun the war with England, America will summon hundreds of millions of Indians to rise in defence of their inalienable national rights. The same summons will be issued to Egypt and Ireland — there is no lack of those who can be called upon to free themselves from the yoke of English capitalism. Just as today America in order to drain the living juices from Europe comes to the fore draped in the toga of pacifism, so in the war with England she will step out as the great emancipator of colonial peoples.”
Without large scale support from workers across Europe, the UK would be strangled within weeks, and such an adventure would lead to large scale reaction imposing itself on British workers. That is why the EU is the minimum scale of politico-economic unit that socialists can see as a viable basis for their struggles in the modern world, and why any retreat into nationalism is reactionary.
The reason that socialists should vote passionately to Remain in Europe is not because they have any more or less faith in a capitalist EU proto state than they have in their own capitalist states, is the same reason that workers in Scotland and Catalonia should vote to remain within their existing nation states. It is that the solution to their problems lies in building the greatest possible unity with their fellow workers across borders, and fighting for solutions on the same kind of scale, and not to be diverted into reactionary nationalist blind alleys, as happened with the division of workers in 1914.