>Gandhi's great insight was that nonviolent resistance is more effective than violent resistance.
Except: that isn't true. Or rather, it's true only in certain circumstances.
>Popular movements pretty much instantly lose their legitimacy when they turn violent
Perhaps, but "legitimacy" and three bucks will get you a cup of coffee. Power accumulates in the hands of whoever controls large numbers of men with guns.
>That some authorities massacre people doesn't refute it.
Actually it pretty much does. In the contest between a nonviolent movement with "legitimacy" and a violent authority without it, the violent authority wins every time.
The few times that nonviolent movements have succeeded, they have done so against a tired power that was pretty much in the process of withdrawing anyway -- the Soviet Union circa 1990 and Great Britain circa 1950.