The "I've got nothing to hide" mental approach isn't a misunderstanding. The author is wrong about that. It's almost exclusively about an intense fear of confrontation.

The alternative mental approach is a forced point of confrontation with imposing authorities, which terrifies the average person (depending on the country and its authorities, that may be a particularly rational reaction). Most people spend their entire lives avoiding confrontation whenever they can. They dread confrontations with a boss, co-workers, a spouse, friends, a waiter, a bully, a landlord, with nearly anybody. It causes immense anxiety for most people and they will seek to avoid it at great cost.

Now elevate it to the level of challenging the divine god-king powers of an omnipotent US federal government (a slight exaggeration) that throws around trillions of dollars like it's nothing, has a history of putting hundreds of thousands of people into prison unjustly in domestic 'wars' (war on drugs, war on crime, war on booze) and murders women and children by the thousands in pointless foreign wars with zero moral qualms (not an exaggeration). Now go challenge that beast head-on and proclaim loudly: you have no right to invade my privacy! Me, the little mouse down here (how the average person actually views their own existence), hear me roar! The average person is afraid of confrontation with their landlord, and they're going to do that mentally? They're going to challenge goliath? No, they're not. They're going to instantly shrink away as fast as they can. When they know there is something questionable about what the authorities are doing, and they fear that confrontation, the fastest way to mentally run away is: I have nothing to hide.

And that's all before we get to the entirely practical time limiting factors. The average person is also tired, maxed out on obligations (work, social, other), mentally stressed. That adds to their reasoning for avoiding conflicts, as conflicts can be expensive and risky. They don't like conflict to begin with, if you add in the pile of risk factors, it just makes it that much more desirable to avoid/evade if at all possible.

The only thing that's very interesting about the "I've got nothing to hide" approach, is how many people fail to grasp what the actual root of the issue is. It's fear of confrontation, not a misunderstanding, not vast ignorance. It can't be solved for, you're never going to convince the majority to be confrontational (they never have been), it will always be down to a small'ish minority of people to fight on their behalf (this is true whether we're talking about the Revolutionary War, WW2, civil wars, privacy, human rights in general, you name it).

The majority will always seek safety in numbers (think about it). I've got nothing to hide, is: I shall camouflage into the herd, nothing about me is particularly special, I don't stand out, I can avoid risky confrontation in this way (the highest % safety calculation for the majority is to hide in the herd; these calculations are made largely automatically, subconsciously, it's a biological function we do as animals), what are the odds they isolate on me (also the calculations for a typical person in Soviet Russia or any totalitarian system on a day to day basis, that's how such people get by and survive). It's an evolutionary survival tactic, it's not newly spawned due to the privacy debate, that's merely one application of it.