If your friends are reasonably bright/open to discussion, but are making the "I have nothing to hide, so why should I worry" argument, and their genuine fear is

If your friends are reasonably bright/open to discussion, but are making the "I have nothing to hide, so why should I worry" argument, and their genuine fear is terrorists blowing up their kids - I've had a little success with the "You might not have anything to hide, but others may." Then remind them that some people may be hiding things for good reason (fear of ostracisation/violence/death) as a result of social or religious reasons, and that if a list like this become public it could seriously affect _other people's_ lives, has sometimes made people take note. Obviously you have to choose your argument carefully.