The analogy that a commenter made here about a plumber entering your home is spot on. Like the locks on a door, the security mechanisms Apple has designed are constructed to thwart breaches on a large-scale (governments) and also on a small scale (your snooping family members).
Protecting it from people who need to service is it does not seem to fit any of these categories; if you cannot trust the Apple Genius in the store, seems silly that this same person would nonetheless trust the probably dozens of people who handled the device before it was finally placed in its box. And, like the plumber, if you somehow want him in your house and you want him to provide expert advice on how to fix your problem yet you fear that he may do something nefarious in the process, Apple does one better than "keepin' ya eye on him" -- it essentially allows you to strip the house of all of your belongings so the plumber has nothing to look at but the sink. And then it lets you put all your things back in. Seems pretty good to me.