One argument is given that the police can use their video, but they don't want the public to use their video. That's obviously a very lame argument.
There is one truly legitimate concern I have about the public video'ing police interactions. Those videos are frequently used in an edited form to make things look bad for the cop. These get posted on the web.
The flip side of this is that evidence is often edited for maximum effect against defendants.
What to do? The cameras are not going away unless devices like that are outlawed. No law or enforcement body can change that. Today I can have a virtually invisible camera on my person that looks totally unlike a video camera. Most cell phones today can take still photos, and many have video recorders built in.
Somebody remind me. Weren't photos inadmissable as evidence at one point because they could be so easily doctored or otherwise used to "quote out of context"? What is the law now?