I keep seeing this suggestion, and it seems not to occur to the proponents that it would simply land someone with destruction-of-evidence charges.

What I want is a system that has two passwords that unlock two wholly separate partitions, one of which is anodyne and the other which is where I keep my private opinions about Big Brother.

Of course, astute investigators might wonder why the accessible partition only uses half the storage capacity of the device; you might wish to make your secret space very small and perhaps use some compression scheme as well. If you have a large amount of information that you wish to keep private, you're probably best storing it somewhere else entirely and only accessing it remotely.