A historian of the sixties explains how 68-69 Chicago riots destroyed the student movement

Todd Gitlin, former president of SDS writes in the Nation http://www.thenation.com/article/166142/will-occupy-embrace-nonviolence
The authorities in Chicago, Tampa and Charlotte hope to scare Occupiers away. They’ve thrown down their gauntlets. These are flagrant insults. And very likely some who show up to stand for economic justice and decency will react not only with indignation and mockery (eminently called for) but in-your-face breakage and belligerence, even though Occupy Chicago explicitly defines itself as a “nonviolent nonpartisan people’s movement.” No matter whether it’s the riot police or the agents provocateurs or the “black bloc” who cast the first stones, under Chicago’s new ordinance, if vandals hijack the demo or damage property, the city could legally force the organizers to pick up the tab.

It’s not hard to imagine scenarios in which windows are smashed and heads clubbed. What happens then—regardless of who started it, regardless of the assemblies’ nuanced arguments about the true meaning of violence—is that the image of the protest becomes just that: violence. Which offends people in living rooms everywhere, many of whom sympathize with the thrust of Occupy. Seeing what gets framed as “violent clashes,” whoever started them, they cringe and pull back. What moves to the forefront of their minds is an association between Occupy and a symbolic amalgam of disruption, inconvenience and the privileged frolic of rich kids. Panicky about the loss of law and order, they’re more likely to vote for take-no-prisoners politicians whose idea of reform is a reformatory.

I was on the streets of Chicago in August 1968 when provocative disrupters among overwhelmingly nonviolent protesters were infiltrated by provocateurs and beset by rampaging police, producing a televised spectacle that had the perverse effect of encouraging a disengaged public to side with the police against what they thought were dangerous and frivolous revolutionaries—even as the Vietnam War declined in popularity. Let there be no romanticizing of those who “upped the ante” toward militancy, indifferent to the fact that 95 percent of America was politically on their right—or of the few hundreds whose stagy vandalism (“Days of Rage”) a year later sounded the death knell for a mass student movement.