Leaderless emergent movements almost always overstep.

There's no regulator to slow down the process, especially if there's a moral fervor about righting some persistent wrong.

Everyone is swept up in the momentum, even as they increasingly lose conviction that it's still justified to the extent the movement is executing on it.

Going against the momentum, against the stampede, now becomes dangerous (you'll get trampled) so you go along.

Only after the mob has clearly and ambiguously crossed the line can everyone go, "oh, yeah… that was obviously too far."

Unfortunately that tends to invite radical over-reactions from the other side.