Where others may have quailed from the looming threat of darkness, they embraced it. Where others reviled the blatant corruption of the Burning Legion, they not only accepted it, they went looking for more. And where others may have listened to common sense and turned from the face of evil, they saw evil for what it was, took its measure and took what it had to give, gladly. It wasn't about corruption, it was never about corruption -- it was about power.
And for the Shadow Council, power was everything.
Formed long before the creation of the Dark Portal and the first invasion of Azeroth, the Shadow Council managed to survive the death of its leader. In fact, it thrived in his absence, and despite the supposed extermination of this dark society, it still thrives today, albeit in lesser numbers than before. But though its direction and leaders may have altered, its purpose has never really changed -- devotion to the Legion, at whatever costs that may entail.