It all sounds very naive to me. Immigration is not some kind of cure for mankind's woes, it puts strain on the UK and will leave behind a devastating shortage of manpower in the countries where people are leaving. Google "brain drain".
Why do you say risk? It's not like we're going to flip a...
Try to think what "left behind" really means. What is the goal in your world?
For me, it is being happy, living free, in a safe and sustainable society. I think this is more achievable outside the EU.