There's no one to sue. But you can sue a union. But their presence is raising important questions about what the movement wants and what it's willing to do to get it. Furthermore, the equation of property destruction with the destruction of human bodies needs to be resisted. But, you know, if you smash the window on a cop car, you got that coming to you.
Violence is the central question in media coverage of the protests.
The obvious reason for this is that violence is interesting, journalism naturally seeks sensational stories, and television accelerates this phenomenon exponentially. For Martin Luther King, Jr., violence on the part of police was, though execrable, almost the whole point. Images of cops beating defenseless blacks or releasing hounds on the marchers were instrumental to the awakening of public opinion and public shame that led to significant civil rights legislation. The media's job was, quite simply, to be there when these things happened. And it is precisely police violence, not protester violence, that could sway public opinion.