They weren't primarily organizing armed revolt.. it was more about the idea that they were articulating moral clarity. They were, in the most credible way, refusing to accept endless delay.
This allowed them to shift the baseline of what was politically tolerable.
In that sense, the movements worked collectively because of a kind of good-cop/bad-cop dynamic. MLK JR offered a path to reform that felt (to some) constructive and legitimate _because_ there was a visible alternative that many people udnerstood as worse.
I think violence is already far to prominent today, but I think successful movements do need both moral persuasion (if morality is still a thing that persuades) and _also_ a credible way of making inaction feel unsafe.