Remember the discussion started talking about bad advice from PC World rather than hiding stuff from customs. That said, I can think of tons of reasons. First, the law requires a ton of stuff to be encrypted. In law, there is a problem with the attorney/client privilege and disclosure of evidence to third parties. There are a number of cases that say that once you show privileged materials to a third party you waive the privilege. If I let US customs read my notes, I arguably can't complain when my opposing counsel wants a similar courtesy.

Then there is the issue of places like China and the theft of IP contents. Many people fear that if they let Chinese customs look at their design, the counterfeiters will be pressing the product before you make it to the hotel and check in. Then there is the issue of politics. Imagine if you are providing support services to someone challenging the ruling party in a country or even worse assisting some group like Palestinians in Israel.

I have a friend who is an Jewish and Israeli licensed attorney helping Palestinians in the West Bank stop Settlers from grabbing their property. He works like crazy to protect privacy because he is afraid that his client's homes would be bulldozed before he can deploy his legal strategies if the Government figured out where he was going.

There are many honest people out there who do not wish to share their position.