I am in favor of a Brexit - I sincerely hope it passes.
I think there is a lot of bullishit and alarmism on both sides, and frankly it's showing up in this thread as well.
The UK existed long before the EU and it did quite well. This idea that the country suffered rolling blackouts and was economically stunted in growth is laughable. The whole world experienced somewhat of a technological and economic renaissance over the past 30 years, and it wasn't because they were part of the EU. And there is no connection with having to accept open borders to get free trade. They're called trade deals and the USA has successfully negotiated lots of them that provide free trade and open borders have never been even in contemplation as part of the trade deal.
As for the immigration issue, I am a UK citizen and I spend a fair amount of time there. Each time I go back, I am amazed at the transformation. I feel the pro-EU side of the debate paints it as racism, but I don't know anyone in favor of a Brexit who just hates foreigners. There are so many in the UK now that it's impossible not to mix and mingle with them, nor do I think anyone believes they are all going to pack up and leave if there's a Brexit. However, the UK is one of the most densely populated countries in the world (excepting small countries and islands like Monaco, Nauuru and such). When people talk about needing a younger generation due to low birth rates... for what reason? Is the UK in danger of running out of people and will have nobody to run public services? No, what people are talking about when they worry about low birth rates are who is going to pay for the welfare spending as the existing Brits age. Well, as people live longer and welfare spending rises, the base of the pyramid has to get a LOT bigger to support the Ponzi scheme. But the problem is if the UK imports sufficient workers to keep it alive... what happens when those people age and retire? Import more? And more? Until there are 20,000 people per square km like in Monaco or Macau? Eventually it comes crashing down and it's a lot better to head these problems off before they become insurmountable.
And last but not least... if being in the EU is a good thing for Britain and for the EU, then if Britain leaves and it turns out it wasn't a good idea, then there is nothing stopping them re-joining. People say it won't be that easy - really? If that is true, it means the EU rules based on spite, bias, vindictiveness and not based on common sense and sensible policy. And if that's the case, better to GTFO sooner than later.
It's sort of like being in a marriage. Do you want to be married to someone that you stay married to because of how much they say they would ruin your life if you ever got divorced? That's no basis for any kind of relationship - social or economic.