Europe needs to do something to reduce the possibility of mass migration (to any country) and if/when this is sorted, there is no doubt that we are better off in Europe and trying to work from within to improve peoples lives, not building the castle walls higher and higher and trying to live on our own.
Britain is so far from being self sufficient, we have to trade with the rest of the world and IF trade becomes harder in Europe, we are making life more difficult for ourselves, just to appease the Tory right wing.
Some of them still believe that Britannia rules the world but, it doesn't.