The sudden hue and cry to bring down the confederate battle flag was sudden and unexpected. Now, the movement to remove statues of confederate politicians and soldiers, rename streets and military installations, and exhume the remains of confederates buried on public land.
It would seem to be political correctness write large, However, the phenomenon is as old as human history -- mass hysteria -- spread beyond localities by social media.
Pogroms against Jews for murdering children to make matzo -- blood libel; witch trials; killing cats as witches's familiars during the black plague (eliminating the creature that eliminated rats); and racist attacks against whoever for whatever are examples.
So, if progressives you know seem a bit crazier than usual -- they are.