The 'christians' (and jews?) were acting as provocateurs. The muslim violence was an over-reaction, but the people that got stuff thrown at them were antagonists. They were not just there. They were pulling a 'My god is better than your god' with various signs, and just being shites. The cops also were pretty nice when they asked them to leave.
Of course the cops did nothing about the violence, but they weren't dealing with peaceful protesters who swore not to fight back, who are trying to make the world a better place at Occupy events. If the cops had actually tried to do their job in this case, they would have gotten their arses whupped, so they didn't do anything. Just like they won't go to parts of Los Angeles. This is what you can expect from them.
They'll bash your head in for smoking pot, but if the other side is evenly matched, they don't go there.
Go figure. Why should they risk their hides for us peons who they are under no obligation to protect? Again, they are there for the corporations, and whoever can afford to bribe them. Exact quote from a prior post. The corporations includes city, state, and federal government. Basically, they are.
