As in all walks of life, there are the good ones and the bad ones. All cops have to deal with more living trash than you or I see in a lifetime. It's surprising more cops don't get pissed at maltreatment and bust a gasket. Every cop in our tiny town (20 cop PD) has been shot or had broken or busted up body parts. And you certainly do not know the exact circumstance or reason for the reaction of the cop in the vid.
What would you do without police to handle the gangs, drugs, drunks, burglars, accidents, etc? A little praise might be warranted for the group, too. Cut them a break in your generalizations, please. There are people in every one of your lines of work that have gone berserk and flipped and hurt someone. They just happen to have more cameras in PD's than most other places. And let's not rush to judgement on this particular lone cop, until the facts are in.