Right. This is a lesson that is utterly lost upon the left. Non-violent protest develops and is effective when the government is influenced by public opinion. That is non-violent protest's power, the power of an outraged citizenry that will either vote (preferably) or force (if necessary) the current rulers out of power. When the State controls the media, is non-democratic, or has a monopoly of power (funny how those three so often coincide), non-violent protests are dealt with very effectively and efficiently by the State. Does anyone really think that the cops in riot gear with truncheons and guns are really being held at bay by the semi-literate patchoilli-reeking hipsters with the chants and the signs? They are not. They are retrained by leadership that is, in turn, restrained by their desire to not be voted out of office. Elmininate the possibility of that and the hippies will find out what "less lethal" is all about.
Or just "lethal".
PS I'd remove Kent State from that list, btw. Outrage about that was effective in changing a lot of things.