I will say just one personal thing about the U.K. decision to leave (and leaving aside the austerity-related reasons which led many people in the North of England to vote to leave, which I sympathize with). The decision saddens me as a science fiction reader and writer.
Growing up on Star Trek, I imagined a future where the people of Earth would finally come together, putting aside our national divisions, to create a whole Earth, united, cherishing all of our people, and ready to step out into a wider universe.
For all its flaws, the formation of the E.U. seemed like a step in that direction. I worry that we are going backwards now, into old mindsets of us vs. them, of hard drawing of national borders, and a xenophobic backlash against the Other.
What country you are born into is an accident of fate. Instead of building more walls, I wish we were reaching our hands out, to help others, especially others in need, cross into our lands freely.