In my opinion, strong encryption should be available to the public, even terrorists and criminals, for two primary reasons, one theoretical and the other more practical.
The theoretical reason is the one that Singh identified as the primary argument in favor of strong encryption: privacy rights. As Singh notes, the Declaration of Human Rights protects privacy and communication from “arbitrary interference,” and this is a notion that most democratic governments seem to support and protect. But at the same time, virtually every government in the world conducts mass surveillance on its citizens which seems to conflict with the declaration of values. Is collecting, storing, and mining personally identifiable communications from innocent people not “arbitrary interference”? It seems that if that phrase is to mean anything at all, mass surveillance surely must be an example.
Of course, one might argue that although it is interference, it is justified by the hopes of cracking down on and deterring crime, securing the safety of the people, and ensuring national security. But this leads to the more practical argument I see in favor of publicly available strong encryption, which is that despite strong encryption being publicly available, crime and terror are no more rampant now than they were prior to the advent of the internet. And of course, as exposed by Edward Snowden, even with strong encryption available, the NSA can still effectively conduct mass surveillance.
Even if strong encryption were outlawed, criminals would still find secure avenues to communicate. For example, breakable codes and ciphers could, in some instances, provide criminals with enough security to pass on time-sensitive information before law enforcement had time to decipher the message and act on its contents. Digital steganography is also a potential subtle form of communication that would obscure messages from law enforcement to stop them from even realizing a message was being sent. And of course, meeting in person is a reliable way of communicating which is much more difficult to wiretap than an email or phone call.