I am pretty sure they are alienating a lot of their customers by having their employees snoop on their customers' computers. The argument you are making is "if you have nothing to hide you have nothing to fear" which is ridiculous.
The example in the story sounds like the doctor had a picture of his grandkids in the bath tub, so of course there is a grey area and it’s terrible if someone is arrested for that. I think that falls under poor discretion and/or badly written laws. It doesn’t mean that you shouldn’t report real “you know it when you see it” porn involving children.
Also, how stupid do you have to be take a computer full of child porn to be repaired at Best Buy?
The FBI is essentially fishing for crimes indirectly through another entity, so it can stay "within the law" itself. Not that this is the only way they fish for crimes these days.
FISA now allows them to do exactly that, and only ask for a warrant after they found the crime so they can use the info in Court. In other words, the warrant is completely pointless now, because the warrant was supposed to stop the government from abusing its surveillance powers.
This is kind of like that, too.