I understand the officer safety aspect of it, I really do, but IMO, the bottom line is this:
We pay the police, and the devices they use. We should be able to listen in on them. I can see giving them a private channel for broadcasting private info during a raid, or like the Boston Marathon incident. But not as in, "We don't have to be held accountable for what we say on this channel", private.
Also, journalists use scanners to be on the scene first. Unfortunately, we are seeing ever-increasing mindless repetition of tweets and other social media blips regurgitated without verification. Hence, a decline in actual journalism, and the puplic's growing distrust in mainstream media.
Let's say you want a law, or mandate that says citizens can't listen in. What happens if they break that law/mandate? Will you get arrested, fined, cops come to your door? Now, let's say the citizens DO stop using the scanners and resort to using Twitter or Facebook. then what? The whole idea and premis behind creating the law to begin with is because information was being released to the public that jeopardizes officer safety and tactial operations, and if someone does that by listening the the scanner, they can possibly get a visit from the local pokies, but what happens when they use twitter? Are police going to show up at your door for a tweet? And please, before you go off on some tangent about how stupid this sounds, realize this is a hypothetical situation, though not so far-fetched.
Maybe you want to advoctae for this law/mandate in the wake of terrorist attacks? In the end we lose more rights over a false sense of security. As if the Patriot Act didn't go far enough.
Some people may think that getting secured lines of radio communication is easy these days with all the advances in technology but its not as easy as you think. Besides the cost of the equipment and the personnel that would be needed to run, monitor and service secured nets for tens of thousands of LE departments there is a very real problem of losing secured radios, leaking the encryption keys, leaking the fills etc. In the military your career turns into a flaming pile of dog crap if you ever lose a sensitive item such as a radio, a fill or encryption keys. Its a very legitimate national security concern. These are all controlled devices. We still have guys that lose this stuff on the battlefield. Now blow this up to a much larger scale to LE agencies and PD's all over the country. Bad idea. They can stick to what they have. The ones that need secured nets like SWAT, SRT, HRT, DEA etc all ready have them. The normal cop patrolling a neighbor hood does not.