Protests are complicated
Some people who are breaking shit and setting stuff on fire may be infiltrators, either right wing, white supremacist, or police.
Some people who are breaking shit and setting stuff on fire may be experienced non-local left protesters who view it as a useful tactic (i.e., Black Bloc).
Some people who are breaking shit and setting stuff on fire may be local left protesters who view it as a useful tactic.
Some people who are breaking shit and setting stuff on fire may be local folks who are just fed up and angry and want to smash shit.
Some people who are breaking shit and setting stuff on fire may be local folks who just let themselves get carried away in a crowd.
Some people who are breaking shit and setting stuff on fire may be local folks who just want to get some shit for free.
Some people who are breaking shit and setting stuff on fire may be just the usual kind of people who like to fuck shit up for fun.
It's quite likely that all of the protests have some mixture of all of these kinds of people. There's a lot of wishful thinking going on here and it goes like this: The people who are doing the stuff I disagree with are not on my side. It's a seductive idea, and one that we'll cling to any evidence to support. But we're all grown ups here, right?
Life is complicated. Protests are complicated. Motives and tactics and actions in the heat of the moment are complicated.
It's never all one or the other.