Because in the event of a Remain vote:

The EU will never listen to us again — we will never again be able to argue credibly for any EU reform. We tried, we even ‘pointed a gun’ at them, we failed, but we chose to carry on anyway. That will have serious repercussions. There will be no change to immigration into the UK from the EU— now or ever. It will stay literally out of control. The EU’s push towards creating “a country called Europe” will accelerate. Britain, the awkward partner, will no longer act as a brake on political union. The EU will feel it has greater authority to stamp on national democracy in pursuit of its goals. We will have accepted rule by unelected officials. There’s no such thing as a qualified remain vote — it’ll be taken by Brussels as a total endorsement. George Osborne may become prime minister We will have accepted the notion that living under our own laws (i.e. that thing called democracy) is now a minority viewpoint and over time will become a fringe viewpoint. Politics in the UK will become ever more irrelevant and will be held in ever more contempt by the people. “Anti-politics” in the UK will grow. So will reactionary (and very unpleasant) movements across the continent. Britain will become ever more irrelevant on the world stage as the EU takes over. The ‘status quo’ (staying where we are now) will have lost. Instead we will remain on a fractious journey towards political union. “When it becomes serious, you have to lie” — Jean-Claude Juncker. This individual and this mindset will have won. Those who championed Britain joining the euro will have won. Those who correctly predicted the euro disaster will have lost. The question of Britain’s membership of the euro will come back into focus: “a logical next step in our membership”. The EU will dominate the continent of Europe ever more. Non-EU countries like Norway and Switzerland will be bullied into conformity. Fear will have triumphed over hope. The essential message of the Remain camp is “Britain is weak and small, it can’t survive, let’s be done with it”. We will have accepted that position. The banks, big business, Goldman Sachs, the international political quangocrats and the vast majority of Westminster politicians, will have triumphed. So will “New Labour” — Tony Blair and Peter Mandelson. We will be told that the question of Britain’s EU membership is now settled once and for all. We will never again have the opportunity to leave. Never. Integration will have gone too far. If you thought disentangling from the EU was difficult now, it’ll only get much worse. The things that British voters have long complained about will still afflict our country. A Remain vote is a vote of confidence in the whole rotten political system. You will have voted for something whose objective (of political union) is rejected even by many/most Remain supporters. Indeed you will have voted for something that the Remain camp admits is rubbish.

And why should you positively vote Leave?

Because you want trade and friendship, but expressly do NOT want political union with 27 other countries. Because you want to enter exit talks that might actually give us something instead of getting 40 more years of the same. You will be returning better democratic control over the politics that governs us. You will break the EU’s anti-democratic strangle-hold over the European continent. You will confirm that Britain is still a country to be reckoned with. You will be moving Britain back to a normal state of affairs — that of national sovereignty — seen as completely normal everywhere in the world except in the EU.

And if it floats your boat: you will also make Nigel Farage redundant.