

If you want to be glib: “Okay then, unlock your phone and hand it to me. Also, tell me your home address, your daily route to and from work, and your last three girlfriends. Don’t worry; you can trust that nobody will ever abuse this access to your life and past, because you have nothing to hide.”
Even if you “have nothing to hide,” a malicious or uncaring actor can use your information to disrupt your life or cause you harm. Police agencies go after the wrong people. Crazy people stalk others. Blackmailers look for opportunities to extort victims. As Cardinal Richelieu supposedly said, “give me six lines written by the hand of the most honest man, I’ll find enough to hang him.”
Google/Facebook/whatever private entity are not innocent. They will happily sell information about you to whoever is willing to pay. Government agencies subpoena data from them, too.
Wikipedia has an easy entry to further reading:
https://en.wikipedia.org/wiki/Nothing_to_hide_argument















Or pacifism?