In a normal company the shareholders elect a board which in turn selects the management of the company. This provides multiple levels of accountability.
Facebook has an unequal share class structure. Mark Zuckerberg, and a few other insiders, granted themselves ten times the votes of normal shareholders.
This unequal share class structure means Mark Zuckerberg's control over Facebook is near total. This is too much power in one hand.
As a result there is a lack of accountability of Facebook to the public markets. One person gets to decide what people do or do not see.