Why are the rights to individual privacy of foreigners any different than those of citizens? I personally believe in a universal approach to civil (and social) rights, with little to no exception (and I certainly would not make airport and customs inspections one of them). From a practical point of view, as soon as you start placing people into different "categories" that enjoy various limits on and degrees of freedoms, your own freedoms (as a citizen) are automatically falliable and can be modified/nullfied at any moment.

Besides that, in the end, all these searches and invasions of privacy are in the name of security, protecting our borders, protecting agriculture, protecting commerce, whatever. A citizen is just as capable of carrying kiddie porn or contaminated soil as an evil foreigner.

Furthermore, in the US your right to re-enter your country of citizen does not extend to a right to carry/import contraband and the like anyway. So I think the argument that allowing searches of foreigners while waiving citizens through it not only a violation of basic rights principles but also very ineffective policy of which no good can come.

All or nothing IMHO.