Although it can be interpreted as such, it's not a sign of guilt, it's a response to the possible threat of immigration officers on a power trip. The vast majority are absolutely fine, but there are some that overstep their bounds or work within an egregious legal framework, e.g. the Brits. If they force you to decrypt your data (as they legally can in the UK), who knows what they'll do with it, especially if you've got proprietary work and confidential business stuff on there.