The most effective response I have personally found to "I have nothing to hide" is: It's not about you. It's about people who do have things to hide. Journalis

The most effective response I have personally found to "I have nothing to hide" is: It's not about you. It's about people who do have things to hide. Journalists and their sources, whistleblowers, dissidents, lawyers and their clients. They need privacy. Therefore, be on the side of privacy. There are of course many other arguments, but this is the only one where I've felt like people I spoke to listened and began to change their minds.