You do understand that, when being discussed empirically, nonviolent protests often includes riots and looting right? Here you go.. I'd also like to add that your own source states that violent protest is effective. And that nonviolient, nonnormative protests are better at garnering public support. They article states the author personally believes those protests may be better at introducing change. Not that it is. They think it might. For a more thorough look into things here's a video that's worth your time and consideration.