And you're missing mine.
At the border, the government of any country has every right to know what you're bringing into -- or taking out of -- the country. It's a matter of a.) security and b.) collecting taxes (tariffs) -- the two fundamental roles of the federal government according to the Constitution.
Accordingly, the 4th Amendment against "unreasonable search & seizure" does not apply at the Port of Entry (or Exit).
In the Interior, your position is justified. At the border, it's not.
The security reason is pretty much BS when talking about diamonds therefore we're down to taxes. So you think just because someone crosses a border their wealth should be up for grabs by the government?