Is there any difference between US citizens and visitors? It just seems like US citizens think those charades are normal and don't question them. In my home country I can just deny getting my devices searched. They might be allowed to seize and seal them, awaiting a court order for searching the device. Which I could appeal. Basically the same process as anywhere else in the country, international borders are not some special place that gives the police superpowers.

Ps: we also don't have some special paramilitary border police. Just regular police stationed at the border.