This point has been debated for quite a while: entire conferences have been held on this topic! Perhaps 20 years ago you would have found plenty of people who agree with you. But the emerging legal consensus, in academia, in Congress, and in the courts, is contrary to your view.

Excerpt from the 6th Circuit's Warshak opinion: "Since the advent of e-mail, the telephone call and the letter have waned in importance, and an explosion of Internet-based communication has taken place. People are now able to send sensitive and intimate information, instantaneously, to friends, family, and colleagues half a world away... By obtaining access to someone's e-mail, government agents gain the ability to peer deeply into his activities."