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Lieutenant General
My experience is that the trouble makers are frequently the police themselves, sometimes police in uniform as reported in article cited above, sometimes police in civvies or other agents of the authorities out to provide an excuse for violence by the police. The public would be safer if the authorities allowed concerned citizens to express themselves. Of course democratic politics might then lead to the end of the career for some politicians.
In small numbers those instances does happen. But lately I've seen on news is that most large cities police forces around the country has cops video recording of the area of where the protesters took place probably use as evidence in case a major break out does occur. In all the police are taking every precautionary measures to ensure safety for the protesters, the public, and themselves. Concerned citizens can expressed their grievances through city halls and state capital buildings, BUT they have to abide by the law lay first, can't barge in there and scream your head off holding a Molotov cock-tale bottle with one hand and megaphone with the other.