Not that I am saying it was justified against people just passively sitting there, but you have to admit it was not exactly Kent State all over again. To be fair, this is the first I have heard of it, so I do not know much about the context or the full extent of the incident; I did find it interesting when I googled it just now that even the article on it in the notoriously conservative Washington Times was fairly critical (and, for anyone unaware of what that means, while I was there I saw a link to another times article on "Obamas denigrate America tour.")

Pretty much never, though there have been some surprising examples of the people responsible walking away unscathed. The Bonus Army is the one that always comes to mind for me: Douglas MacArthur ordered the army to attack (twice,) George Patton led a cavalry charge against a tent city occupied by veterans and their families and both men went on to fame and glory in the Second World War a decade later.

Of course, all of that goes out the window as soon as any protestor initiates violence, and even defensive violence can destroy public support if it is not VERY CLEARLY self defence. At that point the moral highground is lost and the protest is guaranteed a status somewhere between the Haymarket Riots and John Browns raid on Harpers Ferry.

You mean insluting and demeaning to the legacy of hippies? I dunno; in retrospect I cannot help feeling a lot of hippies were just spoiled middle class draft dodgers who wanted to get wasted and laid, and as soon as they no longer had to fear the draft they bought in, piled on and sold out.