The quality of journalism for NPR has gone downhill so much.
A real "protest" is inherently violent. Your are encouraging the state to use it's monopoly of force against you. Your goal is to ensure that others see the state using force needlessly against you. When others see others using violence against you they begin to reconsider the conditions that put you into this situation to begin with.
So using the police as a tool against protesters only proves them right. A protest should never be met with violence, unless you want to encourage more action from protestors.
In other words the police are the wrong tool for the job. The police absolutely should not be involved in protests. This is a great job for social workers.
Riots on the other hand should be met with police action. However, if you have a riot then that means you didn't hear the demands of the people to begin with. If you make it to a full blown riot you have MESSED UP.
The whole philosophy behind protests is really easy to understand. Spend a bit of time reading Civil Disobedience by Henry David Thoreau, a little Ghandi and then you start with a lot of Martin Luther King and Malcolm X to understand the philosophies behind American protests.
People like to give examples such as the civil rights' movement as the effectiveness of pacific demonstration, but that was just a good tactical decision made by Dr. King and other organizers, since they knew that police was ready to kill them at any excuse. In the case of black leaders of the time, any demonstration, even a pacific one, was able to make them subversive to the system.