As public servants and public employees, everything an officer does in his official duties is a matter of public record. When that record is a written record that the officer creates, they have control of the story and how it’s told. When it’s on video, the story unfolds (more or less) as it actually occurs, so they can’t spin it in their favor if they do something that puts them in a bad light.
See I think this is where the discussion goes wrong. The police aren’t public servants. They serve the govt primarily and its interests. When the govt is corrupt the police become nothing more than mob enforcers.