The only reason a sane left leaning person could have for staying in the EU is they fear what a muddled loony bin of 24/7 Surveillance and check points we will become and are becoming anyway. The EU as a construct is now ridiculous torn by nationalism and possibly German Ordo Liberalism that is in danger of giving the UK’s neo Liberalism a good name.
Britain is run for a minority who want to deny the young the advantages they had – free health, universal pension, returns on savings, free education, welfare safety net & peace, Common Market and security. Together with corporate, rural, oil, bankers and other sponger groups. Nonetheless this minority added with UKIP voters is over 50% of those who will vote so I would not rule out BrExit. The BrExit campaign itself is a conceit the UK can pretend Globalisation does not exist and that it is capable for delivering an immigration free Britain.
Essentially the issue is neo Liberalism. Issues with extra protection for rabidly authoritarian main parties in the UK are almost moot since they seem to have no trouble pushing their proto fascist agendas with ‘all’ party support. Of course with 95% supporting parties* committed to the cause of choice less joyless neo Liberalism BrExit is a minor issue albeit I am slightly in favour if only to show the EU free migration are meaningless in what ails the UK.
* SNP Labour Liberal Democrats Conservatives and UKIP