It's meant to be disturbing to garner more publicity for the Black Rights movement.
It's just a thousand pities it was filmed!
It is a thousand pities that more arrests aren't filmed even if it is only to protect the police themselves from false allegations. I have witnessed the police being over zealous with somebody who has done nothing wrong except keep asking why they are arresting them when they have done nothing wrong. It was a black man and whilst they might have had a reason to arrest him that we knew nothing about, they waded into him so as to knock him to the ground. He wasn't going anywhere, he wasn't abusive just bewildered and they hadn't even tried to handcuff him. The crowd were equally bewildered but just threatened to arrest anybody who tried to speak to them. I have also seen somebody who has been beaten up in a police station, had a solicitors assistant come forward to act as a witness to say the victim had not been acting out and then had to withdraw it because her career would be stopped in its tracked and she couldn't afford to take the chance.
That said, there are thousands of good police officers out there who are hurting because of the actions of a minority of rogue officers. There does need to be a debate about how to support police officers in policing and restraint but they have to understand that people dying should not be at their hands. If restraint is needed, it should be for the least amount of time until they get the person handcuffed, wrists and ankles if necessary. Anybody yielding a weapon should expect the use of pepper spray or taser regardless of their medical history and there should be lengthy sentences for those that cause any injury to a police officer. I am not a bleeding heart liberal for a criminal but a civilised society would not want to see anybody given the death penalty before they'd even had a trial.