I think it'd be fair to ask which EU migrants though. I have no doubt that skilled migrants who earn good money will pay in more tax than they take out. But if they do unskilled, low-paid work - especially if they have children - then in pure monetary terms, they will get more out than they put in. I know that because I do low-paid, unskilled work and so I know the in-work benefits you can get from the government. It's more than the tax you pay in (I know, right, string me up!) and that's before you add in using the NHS, schools, etc.
Now, I don't have a problem with immigration. I don't care if I'm working alongside someone from Poland or Portsmouth, as long as they ain't a qunt. But I think, in the main, the people who want us to leave over immigration want to cut down on unskilled migrants who work low-paid jobs that any British person could do. And, as I said in a previous post, other than fruit picking type farm work (I don't know anyone, British or foreign who does this, but I'm told it's mostly foreigners), I don't know of any jobs that British people don't/won't do.