Is it Mr. Sinister with his many clones and ever increasing importance since Judgment Day? Is it Orchis which is responsible for the current Fall of X? Or is it the Quiet Council as a whole with its many f*** ups including not dealing with the Orchis threat until it's too late, giving Beast carte blanche to do whatever he wants, giving such trustworthy individuals like Sinister, Mystique, Destiny and Shaw governmental power to undermine the foundations of the country etc? Or maybe it's Moira who was turned into a literal plot device to set up the era and later comically turned into a genocidal bot and from the looks of it she will play an important role in Krakoa's demise.