I remember there was this quest in BG2 with the circle of druids. Same shit, druids going crazy killing everyone around them. Not sure why they were doing it but if i forgot why it must have been something among the lines of ' we are baaaad". The only difference being kagha doesn't kill innocent people. She needs someone else to do it for her. And tbh no one knows if they are innocent.
About Shadow Druids: they are evil druids that think the only way to preserve the natural order is getting rid of civilization altogether killing people and taking away the means sentient races use to impose their will on the world. They are basically violent ecoterrorists.