Every time I taught a class of newly hired police officers or newly hired dispatchers, I always emphasized that everyone has a scanner these days. I told them that not only are their coworkers on both sides of the mic listening all the time, but so are everyone's supervisors, police chiefs, 911 bosses, a whole of tape recorders, and the entire public. We spent a lot of time in class dealing with issues like proper behavior and communications etiquette. Those problems were much more common and troublesome for all concerned than any fears about officer safety from a suspect with a scanner.
The subject of the bad guys with scanners always came up, but the only time we ever had actual problems was the occasional gang of thieves who used scanners to listen for police dispatches so that they could be far, far away when officers were sent to investigate a burglary or larceny in progress. But they were usually too confident for their own good and bragged about the scanners. Sooner or later someone would drop a dime on them. Once we (police and dispatch) knew what was happening, we would dispatch everything by phone, or in more recent times, silent dispatch via MDT or by cell phone. They'd get caught every time.
Those that are hollering about endangering officers by providing a RR feed really have no clue what public safety communications and law enforcement training and procedures are all about. They're right up there with the nuts that think it's easy to shoot a gun out of the hand of a suspect when he's pointing it at someone.