Laptop searches at the border

I know this is a pretty old issue but it's one that has bugged me since I first heard about it. The US Department of Homeland Security apparently has the right to seize your laptop or other electronics that are capable of carrying data when crossing the border. They can then take a full copy of your hard-drive. This invasion of privacy is all being done under the guise of protecting the country from criminals and terrorists.

The problem is that any moderately competent criminal or terrorist knows this is happening and won't carry their data with them now. It's incredibly easy to take your data, encrypt it, and make it accessible from any machine with a connection to the internet. Once they've crossed the border they can grab a copy of the data and decrypt it. Even more so the data can be encrypted and hidden in plain-sight for later access.

I assume the government knows this. Assuming this, why is the government doing it? Is it a dragnet for the stupid criminals, ones who pose no real threat to us because they're dumb enough to be caught by these tactics?