Because we give special powers to use force to the police that most of the rest of us do not have, the police need more scrutiny and accountability, not less. However, the police tend to fight this accountability at every turn -- in particular, they tend to want to ban any filming of their public activities, even if they have to do it through violence. Likely, this is because every time a video surfaces, it seems to contradict the cover story the police involved have agreed to. I am all for mandatory surveillance of police.
Update: Here is a fun search. Google: "Video Contradicts Police Report" and see how many different hits you get.