"I have nothing to fear because I have nothing to hide."
Cool. Now, can I have your wallet/purse? Also, get naked. I want to see what you're hiding under your clothes.
And you can forward your medical record, along with your business emails to me as well.
Because you have nothing to hide....
The best comeback to this is usually asking if they have drapes/shades for their windows at home. I think I read that in a CCC guide to talking about privacy/security somewhere. At least that has lead to somewhat interesting discussions and the occasional moment of "you might have a point".