You have a First Amendment right to free speech. You do not, however, have a First Amendment right to trespass or set up a hobo camp. This is the problem with the Occupy protesters, well, besides the fact that most of them don't seem to know why they're protesting. They believe the law applies to everybody but them.
They scream at the police, threaten them, flick lit cigarettes at cops, deliberately back into police in riot gear, block traffic, refuse orders to move, and do everything humanly possible to bait the police. Then predictably, when they get what they've been begging for, whether it be a baton to the body or pepper spray to the face, they play the victim. It's like watching people run around in the middle of a busy freeway hoping to be hit by a car so they can claim their First Amendment rights were violated. When the cops go up against this sort of rambunctious mob that's doing everything possible to create a violent clash, your sympathies should always be with the police.
That brings us to UC Davis where the Occupy mob had set up tents and refused to take them down. Then they were asked to move by the police -- and they refused. At that point, they sat down and locked arms to keep the police from moving them. All of the protesters knew they were going to be hit with pepper spray and they could have simply gotten up and moved. It was actually safer for everyone involved, particularly the police, to spray the protesters first -- than to risk injuring them by trying to slowly pry them apart, while other protesters could get access to the officers' backs. Pepper spraying those protesters in the face was absolutely the right thing to do.
Again, the problem wasn't the police; it was that the protesters thought they should be allowed to break the law with impunity. They learned they were wrong about that. That's a good thing. When people break the law, the police need to be allowed to use as much force as necessary to get everything under control and it's too bad that these police officers, who did exactly the right thing, are being vilified by unethical people for the sake of politics. In actuality, cities across the country could learn a lot from UC Davis. Had the rest of the country forced the Occupy protesters to obey the law from the beginning, including using pepper spray where necessary, it undoubtedly would have led to a lot less vandalism, violence, and women being raped by Occupy protesters.