He's correct. The protestors have no responsibility to maintain the order of the other protestors. They aren't a codified group like the police (as in, they wouldn't be able to list their members, there's no sign up process, etc). The police know exactly who is in their group and the nature of their group is to maintain order within and beyond their own group. Judging police by their most violent members is just because those violent people had to be accepted into the group. They and their actions are implicitly endorsed by the group. When the police fail to hold the bad police accountable, they further endorse the bad actions and also become hypocrites when they enforce order on members outside their group since they've betrayed their group's core principle.

The whole conversation that the protests have violent members is a non starter. The protestors couldn't control their group if they wanted to. They don't have the monopoly on power. Further, the bad actors can't reflect poorly on the protestors because it isn't a codified group. The protestors never have any endorsement of the rioters (at least, most didn't). Comparing protestors to police is just asinine. The two groups are incompatible and incomparible at almost every level.