The idea of perfect security is a tantalizing one on the surface. It guarantees anonymity and protection from unwanted attention; it facilitates and protects a bedrock of democracy, that being freedom of speech. Altogether, it's no surprise that, in the interest of preserving the core values of democracy, people would want perfect security implemented for their digital communications. However, with perfect digital security comes a price, one that society may not be willing to pay.
As Simon Singh argues in his The Code Book, once PGP became a widespread method of encrypting civilian communications, it became clear to the American government that such a tool could be employed by malicious entities to mask their activities. In this vein, Singh provides two extremely compelling arguments for why perfect security may not be in the best interest of the people. First, he presents the idea for evidence collecting in a court of law. Here, Singh provides evidence that, during the 1920's, police forces actively made use of phone wiretaps to listen in on communications and gather incriminating evidence. These practices were upheld by the Supreme Court and were widely accepted, and thus helped the police do their job more effectively. With the advent of digital communications and perfect security, the police would lose this avenue of gathering evidence, stunting their ability to collect evidence in a discreet and non-invasive fashion. By doing so, police would be forced to gather evidence physically, which may even put lives on the line that don't need to be at risk in the first place.
Secondly, on a national security level, Singh also shows how international and domestic terrorist groups have used and will continue to use modern encryption technology to keep their plans and communications private and untraceable. Using examples of events like the Tokyo Subway Gas attacks and even the computer of a World Trade Center bomber, Singh creates a dark picture where terror attacks are able to be planned and executed with little in the way of countermeasures, which ultimately puts innocent lives at risk.
As such, it's clear that while perfect security is attractive on the surface, the inability for the proper authorities to covertly access information when the need arises puts innocent lives on the line. Altogether, its a steep price to pay for not wanting anyone to read your emails.