He just has more than 50% voting rights, which should never have been allowed, and should be one of the things that SEC should look at if/when any kind of antitrust probe is done. It leads to deviant behavior by public companies.
Edit:
Some people below are looking at it below from a purely investor standpoint.
I'm not an investor in FB and own no stocks.
I'm looking at the behavior of FB which IMHO is purely due to Zuck, him being unethical (as someone else has also called out below) and the fact that he has unchecked power in how he is running FB. Like in a Government, the Board is supposed to provide the checks and balances in a public company. Unfortunately, due to the voting structure the Board of FB is 100% impotent.