The EU is destined to fail, they cannot manage basic financing, they threw shitloads at Greece without keeping an eye on it and look what happend, the UK is better out of the EU anyways, less migrants.. Even Sweden has the same problem.
Migrants add to the workforce... but... the UK is physically restricted. It's not a large country and it's not one where hundreds of millions can live and work side by side.
The EU, like the United Nations, is a great concept but with each country having their own priorities and different needs, it's tricky to make it effective across the whole continent.
For that matter, perhaps the EU should take on more of a role like the UN and perhaps draw away from the economic, semi-judicial and political side of it in the core.