[andos]

The International Declaration of Human Rights establishes secrecy of correspondence as a basic human right (article 12). It is echoed in the constitutions of many countries.

Shallow packet analysis is akin to reading the address of a letter in physical mail. It does not violate the secrecy of the message. When you sign up for an ISP or create a GMail account, you allow the company to inspect your correspondence and they assure you they will keep it secret under the terms of the law. The agreement is binding. You can sue if your communication is arbitrarily violated.

The content of packages might be subject to customs and taxation. Goods are not correspondence (from the p.o.v. of those laws).

Of course, laws are written taking good faith as a premise...