An eye-witness in Bristol (England) describes how a few hundred very angry protesters started a violent riot after a peaceful protest (against repression by thugs) of 3,000 people.

We on the left who denounce injustice need to keep the violent protesters at a distance, if we can't convince them to contain themselves on the occasions of our peaceful protests.

I understand why marginalized people can burst into anger, because I have done so myself. They have a lot to be angry about. But they need to develop the self-control needed to win their fight.