I'm no supporter of violence.  Over my lifetime I'm participated in many marches and protests....all non-violent.  To be sure, there's a leftist element, who support and employ violence.  I condemn them, just as I condemn violence from the ault-right, white supremacists and white nationalists.  During the Civil Rights Movement days and the anti-Vietnam War days, protesters actually participated in training to prepare ourselves to remain non-violent in the face of violence.  Non-violent protest IS effective.  As you say, meeting violence with more violence only escalates into disaster as we saw with the automobile attack in Charlettesville.  regards, Gary Crum