I would agree with David's rationale for leaving but also agree with Outlaw's view on the immigration file. Here is what I wrote elsewhere:

"The United Kingdom's immigration troubles are primarily the result of its post-war intake of Commonwealth citizens, its welcoming approach to migrants and refugees and its lack of immigration enforcement. Enoch Powell's "Rivers of Blood" speech happened when Poland and Romania were still members of the CMEA and Warsaw Pact...

2001 to 2011 is a key period in UK immigration history. During that time, the number of Polish residents surged by some 10 times. However, in 2010, Eurostat observed that of the UK's 11.30% foreign-born residents, 68% were non-EU. In 2014, the UK's ONS observed that some 1.1 million UK foreign-born residents were from the "new" EU countries of Poland, Romania and Lithuania, compared to more than 2.1 million from the Commonwealth in South Asia and Africa, even decades after de-colonization. Yet the number of "new" EU residents is actually down 1/3 from its peak around 2004-2007. Moreover, between 2001 and 2011, the White population of the UK grew by 1.81%, compared to 75% for the non-White population (ONS). Lastly, the focus on the Poles is curious given that the UK actively recruited Polish laborers after both world wars.

This data tells us a few things:

1. There is emigration by White Britons from the UK (typically to Canada, Australia or New Zealand)

2. EU citizens from East-Central Europe are barely keeping up with the pace of emigration from the UK and have a tendency to return home or leave the UK based upon economic conditions

3. If non-British EU citizens were all expelled from the UK, the British population would actually have a much higher percentage of visible minorities

4. Not only are Asian and African Commonwealth citizens still arriving in the UK in large numbers, but they are more likely to stay than EU citizens, and continue to outnumber EU residents by 2:1

5. Brexit will not necessarily impact Commonwealth immigration or refugee policy

6. The EU has poorly handled the flow of non-EU migrants and refugees, but then again, the UK has accepted them in the past and continues to do so

7. As with Sweden and Germany, migrants are drawn to the UK not because of its EU membership but because of its lax policies and generous benefits which are national and not supranational in nature

8. Poland's economy is doing relatively well, yet Poland is refusing to settle more than a token number of refugees and is not attractive to the denizens of Calais' "jungle".."