it's not a protester's job to uphold the law and "protect & serve"
What a completely asinine thing to say.
First, if protesters don't want to be included in the same light as those doing the evil deeds, then they should be very inclined to differentiate themselves from the criminals.
Second, it is every person's right to speak out against crime and destruction. That is what a civilized society is based on. If I see someone being beaten to death in the street, I have a moral obligation to do something - at the very minimum to call the authorities. Some municipalities even have laws to this effect on the books.