The cell phone, complete with camera and upload ability is carried by nearly everyone the police meet. Not so for the computer - ever tried to use the web cam on the lap top to film something out of a window or on the street? Pretty awkward. The regular camera has been around for decades and the police are used to those, see them, and often take them for evidence, but they are not carried around by the majority of people - and haven't ever been carried by the majority of people. Tablets are huge compared to the phone and make filming both awkward and obvious and again, most people don't have one on them all the time.
The danger to the police is that while they are focused on the guy with the camera filming their arrest of some citizen, everyone within sight can be filming and uploading their rights violations, overly aggressive behavior, etc. The media guy with the big camera, they've got a plan to deal with him. The five hundred eye witnesses? They have a plan to deal with them. The incontrovertible cell phone video showing their behavior is the problem. They have been living in a world where the court, prosecutor, and judge accept without question that the police officer's testimony is true. So after the arrest, the cops get together and make up a consistent story that justifies their actions, and fits the evidence that they gather. Since it is the job of the police to investigate the crime and tell the court and prosecution what happened, they can get the evidence to read any way they want it to read. There is no one looking at the crime after the police unless the citizen accused has the resources to do so with private investigations, private autopsies, etc. The universal presence of video endangers the beat the fuck out of some suspect perk that many, not all, in law enforcement have enjoyed. It threatens their reputation by providing independent evidence that may very well controvert the story the police tell. No other technology does this.
Once the brick feature is added to the phone, it will not be long before technology is developed that can brick a selected list of cell phones within an area. The cops can then pretend ignorance as the cell phones actively being used during the protest brick, while others, not being used, are left alone. Film the cops, brick your phone would spread through the police departments like wildfire. After the event is over, then the phones on the list can be un-bricked. Police would then be safe to make up what ever story justifies their actions and make sure that the evidence they find fits the story.
It's not paranoid. Look at the published police attitude, the rise of no-knock SWAT team served warrants, and realize that citizen cell phones have played an important role in revealing the bad operations with in the police force. Many police do not want this scrutiny and many are afraid of it because they know that if everyone knew how badly they acted as cops, they would be unemployed or in jail.