To all cop-bashers: here is one of several vids showing the NYPD warned [s]hippies[/s] protesters that they would be arrested if they marched on the bridge.

The first amendment does not allow you to block public roadways and emergency vehicles.

From NY Times.com:

With the Internet bursting with videos showing various interactions between the police and protesters from Occupy Wall Street, the New York Police Department decided to add two more.The videos, which were released on Sunday morning, show the police issuing two separate warnings to marchers who were either poised to cross the Brooklyn Bridge on its roadway, rather than the pedestrian walkway, or had already begun doing so.
One of the videos shows a police official warning protesters that if they crossed the roadway, they would be charged with disorderly conduct. His remarks were met with chants of “Take the bridge, take the bridge.” Seconds later, the protesters begin marching across the bridge, accompanied by cheers.
The release of the videos seemed to back the police’s contention that it was the marchers’ choice that led to the police arresting about 800 people. Many protesters had contended that the police had tricked them by allowing them onto the bridge, and even escorting them partway across, only to trap them in orange netting after hundreds had entered.
SOURCE & 2nd VIDEO: http://cityroom.blogs.nytimes.com/2011/10/02/police-gave-warnings-at-bridge-videos-show/