Encryption if it is an available technology is tough to de-justify. The best justification for not encrypting in American law enforcement is that open broadcasting was part of the original fabric of police radio communication technology.
Early AM radios were capable, indeed marked with tuning guides, to specifically tune into city wide police broadcasts.
You bought a floor radio and it was expected that you would be able to listen in to police calls as easily and directly as you would to Amos N' Andy.
However unintentionally and however wrought by lack of technical sophistication this was possible, it's because of this that open public safety broadcasting has been a fundamental component of policing, reflective of our culture's commitment to individual liberty and our angst against the potential for government tyranny and totalitarianism, for most of time.
There are excellent reasons to not encrypt if you first accept American exceptionalism as a real thing in terms of freedom and liberty.
Any other nation on earth with the technology to encrypt its public safety communication would logically and immediately seek to do so -- assuming affordable. The same cultural consideration we have in the USA simply doesn't exist to such level elsewhere. Even early UK radios probably had the ability to listen in to police calls, but they never had the American spirit that led to us splitting up from them in the first place.
Open public safety communication is one of America's unappreciated birthmarks. It makes little sense to foreign countries who balk at our liberties and independence. I would expect encryption to swell within all other nations, but I would expect the fight to NOT encrypt to roar in the United States.
Like anyone reading this, I am not optimistic. What I have concluded and what I am now promoting is a flat-out balls-to-the-walls replacement for police scanning, which would involve the evolution of a parallel human network of enthusiasts, working journalists, activists, and good people roaming or spotting in their cities and regions, and reporting on public safety drama in a very concentrated and channeled way. These spotters would have their own openly broadcast radio network that would be scannable by regular people everywhere and anywhere.
By Dave for for BuffScan.