I think that arguments for leaving the EU based on concerns about immigration are implicit calls for a rethinking of the EU social contract with respect to freedom of movement.
It's exactly this idea that discussions predicated on group identity are somehow outside the realm of legitimate politics that leads to the very resentment that made Britain leave the EU.
It's a shame, because if the EU had treated this issue as a political one, subject to compromise and regulation, they'd have been able to come up with a political solution. Instead, a lot of people treated this issue as a moral crusade and provoked a huge, destructive backlash.
God, homo sapiens is doomed.