Excellent points in your posts. When I woke up this morning, my first thought was about this story. It should bother everyone to no end. The police abridge a man's Constitutional right to protest peacefully (a plastic sword is not a threat last time I checked, neither is wearing a McCain/Palin T-shirt or a Batman suit for that matter) and going with the logic of “they arrested him for his own protection” you have just entered the arena of the rule of anarchy. The anarchist always wins because they are always the greater threat than the law abiding citizen who should have the freedom of speech and expression in a public arena to be heard also.
(I also might add that if the cops indeed did anticipate lawlessness or rioting in that particular crowd couldn't someone cry “racism”?)