Of course, but they have the right to know what you are bringing in, this can involve searching people, it's a practical necessity.

Try entering your country with a piece of nuclear grade uranium.

I know some people's online comments are pretty toxic, but I'm struggling to think of a scenario whereby a Twitter stream or Facebook timeline could be used to make a 'dirty bomb' --and I'm not having much luck.

Could you help me out here?

I'm sure you are aware that their justification is to help determine if people are linked to dangerous groups or not.

Personally I wouldn't go that far but still, my point is that: not being searched at the border is a priviledge, not a right.