Journalist Glenn Greenwald, love him or hate him, offered attendees at his October TED talk a bulletproof argument (as far as I can tell) against the "nothing to hide" argument.
"Over the last 16 months, as I've debated this issue around the world, every single time somebody has said to me, 'I don't really worry about invasions of privacy because I don't have anything to hide,' I always say the same thing to them.
I get out a pen. I write down my email address. I say, 'Here's my email address. What I want you to do when you get home is email me the passwords to all of your email accounts, not just the nice, respectable work one in your name, but all of them, because I want to be able to just troll through what it is you're doing online, read what I want to read and publish whatever I find interesting. After all, if you're not a bad person, if you're doing nothing wrong, you should have nothing to hide.'
Not a single person has taken me up on that offer. I check that email account religiously all the time. It's a very desolate place."