To some degree I understand the cop's position. The internet is an insanely dangerous echo chamber. The vast, VAST majority of police interactions are not that. The vast majority of police interactions are well-meaning officers maintaining public order. This doesn't excuse the interactions which are unrighteous and deserve to be exposed, possibly including the interaction that these people were protesting. The office…
It's not the cop's job to do prevent this video from getting onto YoutTube. We have a whole SLEW of legislative channels that could be used to "protect" cops from people recording them. Don't want videos of cops being posted on the internet? Contact your local representative and have them sponsor a law.
Also, in an environment in which trust with the police has been eroded to the point of rioting because people feel the cops are dishonest and hiding bad behavior, admitting on camera "I'm trying to hide my behavior from scrutiny" is about the worst thing you can do, and will get a national publication to pick you up.
The cop has a police union, qualified immunity, and the entire law enforcement segment of the government to protect him. It's assumed that whatever his report said happened is what happened. Protesters only have cameras to prove their side of the story.
(edited for spelling/grammar mistake)