Not all migration from EU states is positive. Many work at a party grade where they aren't contributing to the economy and there's no reason we couldn't attract the higher paid ones if we were outside the EU. It's not as if we have no migration from non-EU countries. Being able to control immigration is imperative to make any decisions IMO. How do you know how many houses, schools and hospitals are required if you don't know how many people will be needing them? Nor is it preferable to absorb them into existing services - we're at breaking point already.
On the other EU legislation, it's not necessarily what is in place now. I do think that much of what they come up with is completely unnecessary and does small businesses no good, but it doesn't directly affect me.
My worry is what could happen in the future. Just as Inners pose that leaving us a risk, I believe that staying in also carries a risk. On immigration, Turkey and Ukraine are likely to be members soon and who wouldn't want to leave those for the far more prosperous UK? There's also a security risk IMO. Merkel invited millions of unchecked migrants into Europe and events in Paris, Brussels, Cologne and Sweden have proved that some of those are les than savoury characters. In 5 years the foreign nationals will be granted citizenship and will be able to move wherever they want in the EU, including the UK. I'm not necessarily saying I don't want them here - it depends on whether we need their skills to fulfil employment shortages - but I'd like to be able to check who they were first and reject them if they posed a threat to British people, society and culture.