Ugh ... “I have nothing to hide”. This is a form of self-deception. It’s not about YOU being evil, it’s about THEM being evil. They could iMessage you from a suspect number, seize your unlocked phone and use the text as evidence that you’re part of some right-wing terrorist organization. It’s a silly example, but it makes the point. If they can’t see what’s on your phone, they can’t twist it into a chargeable offense; and they will do this. The “I have nothing to hide” argument proceeds from the naive supposition that the government is inherently good, means you no harm and is there to protect you; it isn’t any of those things.
It is actually not such a silly example. Several years ago, government agents broke into a CBS news woman's house, installed a fiber channel cable, physically broke into her Mac computer and installed extra hardware key loggers to watch what she was writing, and, it was discovered when her computer was examined by forensic IT specialists, also installed some hidden photos deep inside a couple of libraries on her hard drive.
In those photographs were some CLASSIFIED and SECRET government documents hidden via steganography techniques inside the images. They had been placed there for future use when and if they government ever wanted to arrest her and wanted a pretext to charge her with spying.
These kind of photos can be sent via email, messaging, or even Facebook.