"I've got nothing to hide" taken literally, is, of course, wrong. Everyone has something to hide. Maybe you made a right turn when there was a "no turn on red" sign. If your car was recording every action you ever took and the car company decided to turn all of that data over to the government, congratulations on your fine! However, we shouldn't take things literally. We aren't, as a society, unable to understand subtext, are we?
And the context of "I have nothing to hide" is: "I have nothing to hide from the system as it currently is and I am taking a calculated risk that the system is not going to change radically any time soon"
The layperson is bad at expressing this deeper concept that they intuit, and why should they be good at it? People are busy living their lives, not everyone wants to become an expert on their own motivations because someone on the internet decided to shove a "You do have something to hide, actually" article in their face.