Sorry for a political post! But this is a pretty big deal to me. The main point being:

I don't get why people would vote to leave the EU.

Leaving will have an adverse effect on our already struggling economy and finances. Every single report, commissioned by the government, or not, says so. If you think we can just negotiate similar trade deals quickly, you'd be wrong. Norway's model would be worse than we currently have, as they need to pay into the EU, implement all the regulations, allow for free movement, but at the same time, there is no representation of them in the EU institutions. The Canadian trade deal is not nearly having the same access to the EU single market. Every deal made with the EU, would very muck likely require us to sign up to the free movement deals. Likely at worse conditions than now, because why would they have a non-EU country on the same deals as EU countries. There is no incentive for them. The same with negotiating other trade deals. The bargaining power of a block with half a billion people is surely going to be higher than that of a small island nation.

Leaving will do little to immigration. I have seen nothing substantially fact checked document that says it will stop people from wanting to go here. Even if it did have some effect, it's likely an adverse effect. It would put up a barrier for lots of professions that we have a shortage of (say, for example, nurses). And at the same time, make it harder for educated people to contribute to the economy, as likely there will be barriers for bringing spouse + children. Queue the £35k earning requirement for non-EU citizens.

Leaving the EU will have an adverse effect on security and border controls. The French are already saying they would put an end to the UK border checks on French soil (to prevent people without authorisation even making it to the UK). A deal currently stopping the migrants in Dunkirk and Calais from boarding Eurostar trains and ferries. Besides that, in the current climate of higher security risks due to terrorism, more integration of the police and border forces is going to be needed. Leaving the EU would make this harder than it currently is, or at least, not easier as would be beneficial.

Certainly, the EU institutions have flaws, and absolutely should be addressed. Britain, as a bit of an outsider, will be much better be able to reform the EU when they're actually part of that. Making the whole block, including the UK, more competitive globally.

But perhaps the most curious thing is why people think leaving is a good thing, is that they think the UK can be better off alone. It's such a selfish and arrogant point of view.

A single country has less clout than a group internationally. A single country needs to do more on its own, taking up more resources, because the burden can't be shared or distributed. A single country would find it harder to fill shortages on the labour market, due to hindrance of people moving around. A single country will find it harder to have access to common markets. A single country will find it harder to be an entry point (for say financial markets) into a group of countries it's not part of.

Instead of being so selfish, work together!