I was at the 1968 convention demos. To some degree they did create a knee-jerk backfire. Henry Hyde got voted in as sort of a response . Certainly the Trial of the Chicago 7 did not endear the protestors to the public at large. Remember, tho, in 1968 the general public had not accepted the deceit of the war as I think they have today. The Q. is, I guess, how to show strength of conviction w/o trashing the city. Remember that during the Days of Rage there was a lot of anti-police animosity that might backfire in the aftermath of 9-11.

Good book covering 1968 just out: Mark Kurlansky, 1968: The Year
That Rocked the World. (Ballantine, 2004).