Massive peaceful protests in Hamburg blocked some of the participants in the G20 meeting. That is good because it makes the participants aware of the popular disgust.

Other protesters rioted, which is wrong and harms the cause. Reportedly thugs escalated the violence.

At a similar international meeting in Genova in 1998, some of the "black bloc" rioters were unmasked as thugs — provocateurs. I wonder if that is the case today in Hamburg.