Organizers of left-wing protests always present themselves as helpless to contain the violent margin, the so-called Black Bloc. Maybe. But that self-presentation would carry more conviction if they announced from the start their intention to cooperate with police. “If you break the law, we’ll turn you in ourselves and testify against you in court” is a message that would have powerful effect. The unwillingness to cooperate with police to prevent violence likewise sends a message about who you are, what you believe, and what your aspirations are.

Martin Luther King changed minds. The Black Panthers hardened minds. Dan Choi persuaded. ACT-UP repelled.

Yet despite this clear compare-and-contrast, the political left returns again and again to the wrong modes of protest. Maybe puppets, chants, and window-breaking are just more fun. Maybe they lack impulse control. Whatever the reason, the behavior predicts the outcome: they lose.